Caterpillars in fall not so bad

walnut caterpillar on pecan branch

Walnut caterpillars may strip leaves from portions or all of the canopy of pecan or walnut trees. However severe damage is unusual and late-season damage rarely harmful to the tree.

Finding a caterpillar on a plant or tree in your backyard can be cause for excitement. But they should be little cause for concern, especially during the fall months.

To most human eyes caterpillars are alien creatures. With their squishy, worm-like bodies, and accordion gait, they are weirdly unique among other insects. Some are large and fantastically showy.  Others have ominous-looking barbs and hairs. And some are skillfully camouflaged, nearly invisible among the leaves and shadows. When gardeners do encounter a caterpillar, reactions range from “cool!” to “yuck!!!”

Caterpillars, of course, are the larval stage of moths and butterflies.  What many good gardeners fail to appreciate, however, is the essential role they play in the backyard food chain.  Birds rely most heavily on caterpillars for food.  Without caterpillars to feed on, we wouldn’t see many of our favorite backyard birds.

But what about the damage they cause?  Most gardeners have been disappointed at finding a favorite flower or tomato plant eaten to the stems by hungry caterpillars. While it’s true that caterpillars can be devastating to crops and the occasional garden flower, most caterpillars, especially those found on trees and shrubs in the fall, pose little danger to the long-term health or beauty of our yards.

yellow bear "wooly bear" caterpillar

The yellow bear caterpillar, sometimes called a woolly bear, is a generalist feeder on weeds and low plants. This one is feeding on water lily.

Spring and summer are times of growth and productivity for plants.  Photosynthesis is at its peak during summer when the sunlight is strongest and days are long. At this time, deciduous plants can withstand 20-40% defoliation with no ill effects; though more severe defoliation can cause stress and loss of vitality.

During fall, growth slows.  Fruits like pecans and acorns fill out, and new growth halts as trees and shrubs prepare for winter.  In a few weeks, leaves will turn and drop, further evidence that plants have little use left for their greenery.

For this reason, caterpillars that feed on deciduous plants during this time of year rarely cause significant harm to our plants. Nevertheless, Extension offices get many calls from worried gardeners about caterpillars in the fall.  Walnut caterpillars are common now on pecans, walnuts and hickory trees.  Various caterpillars are active on our many oak tree species.  Hornworm caterpillars and woolly bear caterpillars are also frequently seen feeding on a variety of ground-hugging, herbaceous plants.  As a rule of thumb, however, none of these should require special attention or an insecticide treatment.

pandorus sphinx moth caterpillar and parasite cocoons

Pandorus sphinx moth caterpillar with parasite cocoons attached. This caterpillar will not successfully complete its development due to its weakened state after feeding by the dozens of parasitic larvae that have now emerged and are resting for their eventual emergence as tiny adult wasps.

Fall is also a good time to observe beneficial predators and parasites of late season caterpillars. Paper wasps and solitary wasps are active now storing up juicy caterpillars to feed their offspring. Also tiny parasitic wasps are attacking and emerging from many kinds of caterpillars.  Look for oval-shaped, white cocoons hanging from the backs of caterpillars.  These cocoons are evidence of an earlier attack by a tiny wasp that laid eggs in or on the caterpillar.  Caterpillars wearing these silken cases are doomed, having been previously weakened by the wasp larvae feeding on their insides.

Gruesome as it sounds, these parasites and the many predators keep caterpillars from being more serious pests. Most years caterpillars are rarely seen in a typical backyard, although there may be the occasional year where certain caterpillars are especially abundant, and may cause defoliation. But our trees and native plants have survived insect attack successfully for many years, long before humans were around to care and worry about them. Unless a tree is under stress from other problems, rarely do caterpillars cause much damage.

flannel moth and sting on thumb

Flannel moth caterpillars, sometimes called “asps”, hide rows of venomous bristles under their long hairs. Avoid touching these small caterpillars to avoid a painful sting (right).

Standing out from the common caterpillar crowd, are some of the stinging caterpillars.  While most fall caterpillars are harmless, a few types of stinging caterpillars deserve our respect.  Over the past month I’ve had a few inquiries about flannel moth caterpillars, known to most Texans as “asps”.  These hairy, odd-looking caterpillars feed on oaks and elms, and yaupon shrubs.  When finished eating they crawl out of trees to pupate on fences and the sides of buildings.  Asps bear a set of barbed spines under their fur coat, that can cause a painful  skin reaction.  Give these guys a wide berth, or be careful to wear heavy gloves if you must handle these critters.

Instead of worrying about caterpillars in the yard, embrace them!  They are providing food for wildlife, and in moderation are a sign of a healthy environment. And on top of that, they are fun to watch and identify.  For additional reading and identification, check out these guides for the gardener:

  • Caterpillars of Eastern North America by David L. Wagner. Princeton Field Guides, Princeton University Press, Princeton, NJ. 512 pp. Still the most comprehensive field guide to caterpillars yet published in the U.S. Beautiful photos of both adults and caterpillars of macrolepidopteran moths and butterflies. A must-have reference with lots of useful information for the serious naturalist and entomologist alike.
  • Owlet Caterpillars of Eastern North America by David L. Wagner, Dale F. Schweitzer, J. Bolling Sullivan and Richard C. Reardon. 2011. Princeton University Press, Princeton, N.J. 576 pp. I thought that Caterpillars of Eastern North America was pretty thorough until this book came out and realized how many species there were to know from just one moth family group.  The Noctuid moths constitute the most diverse Lepidoptera family, and in this guide they are covered along with three other related families now called owlet moths.  Another beautiful guide from David Wagner and colleagues, with stunning photography.  Alas, not a Texas guide, but still quite useful in helping identify moth caterpillars in the eastern half of the U.S.
  • Caterpillars in the Field and Garden: A Field Guide to the Butterfly Caterpillars of North America by Thomas J. Allen, James P. Brock and Jeffrey Glassberg. 2005. Oxford University Press, USA. 240 pp. When it rains it pours. After many years with few references to caterpillars, this book and the Wagner book both appeared in 2005. This volume focuses almost exclusively on butterfly larvae, which make up far less than half of all caterpillars; but it is well done and will be useful for butterfly gardeners and those wishing to supplement their knowledge of the lesser known life stages of butterflies.




Getting tested for Zika

doctor and patient illustration

A doctor is your best adviser when determining whether to get tested for Zika, and what tests you need (CDC).

So you and your significant other are considering whether to get pregnant; but the summer’s headlines about Zika virus and its effect on developing babies has you worried.  Or maybe you’ve just returned from traveling to an area where Zika is active.  You’ve not experienced symptoms of Zika, but you’ve been around others with the disease and you know that 4 out of 5 people who get Zika show no symptoms.  You wonder if you might be infectious to your spouse or partner (Zika can be sexually transmitted). In both cases a test to see whether you might have Zika sounds like a good idea.

So are there tests for Zika?  And if so, which one is right for you?

It turns out that there are multiple kinds of tests for Zika, although no one test is consistently definitive.  The RT-PCR test (Real Time Polymerase Chain Reaction) test is the go-to test used by doctors to see if you have an active case of Zika.  It can be used to test blood serum, saliva or urine, but generally is sensitive only to viral levels present during active infections (first 5 days of illness for blood serum, 2-12 weeks for urine).  Its primary advantages are lower cost and speed, with results available as soon as the same day.

After illness has passed, doctors must rely on tests that look for the presence of antibodies left over after the body has fought off the infection.  A test called IgM-capture enzyme-linked immunosorbent assay (MAC-ELISA) can detect whether IgM and IgG antibodies are present in the blood serum for several months after infection.  Unfortunately, these tests can also react to antibodies from other mosquito-borne viruses, like dengue fever.  So additional dengue-specific tests (PRNT) may also be needed to confirm whether the person has been exposed to dengue or Zika.  These tests are more time consuming and expensive and may require up to a week to perform.

zika rash

An itchy rash is one of the symptoms of Zika infection brought on by a mosquito bite (Photo by Jackie Thornton).

Your doctor or public health office is the best authority to determine what type of test you might need.

So should you get tested?  Unless you live in south Florida, or unless you or your sex partner have recently traveled to an area of high Zika risk, the chances that you have been exposed to the Zika virus is extremely low.  In fact, the CDC does not recommend Zika testing for asymptomatic men, children or women who are not pregnant.

Zika testing is currently being provided free by the Centers for Disease Control and regional public health laboratories, but only for the following people:

  • Those with more than one Zika symptom who have traveled to an area with Zika infection or had unprotected sex with a partner who has traveled to such an area within the past 4 weeks;
  • Pregnant women who have traveled to a Zika area during their pregnancy, or 8 weeks before conception, or who had unprotected sex with a partner who spent time in such an area;
  • Those with Guillain-Barré syndrome with Zika exposure history;
  • Infants born to a woman with a positive or inconclusive Zika test;
  • Infant born with microcephaly by mother with Zika exposure history;
  • Those with Zika symptoms and who may have had an alternative mode of acquisition like a blood transfusion or organ transplant.

Women who think they may have been exposed to Zika, and who want to get pregnant but do not meet any of the above criteria, are not being tested now by the CDC or public health agencies.  Instead, if you fall into this category you are advised to avoid getting pregnant for two months and practice protected sex for six months.  One of the reasons for excluding non-pregnant women is that testing laboratories are currently backlogged with high priority cases.  Even if you meet one of the above criteria, test results may take up to 4 weeks to be received.

There are private laboratories (Viracor, LabCorps, and QuestDiagnostics) that will test blood and urine for Zika through your private physician, with costs ranging from approximately $165 for PCR testing to $700 for IgM and IgG testing.  If you opt for this route, you will bear the cost of testing and will have to proceed through your own physician.

As of 16 September 2016, there were 79 cases of locally acquired Zika in the U.S.  All of the locally acquired cases came from the south Florida/Miami/Dade County area.  So far there has been no local (non-travel related) transmission by mosquitoes of Zika in Texas.

[Thanks to Dr. Robert W. Haley, University of Texas-Southwestern, for some of the background information for this post.]

Girding our loins for emerald ash borer

Emerald Ash borer
EAB training class screen shot

Screenshot from the new emerald ash borer online learning module.

The emerald ash borer (EAB) that has devastated ash trees throughout the Ohio River valley and Great Lakes region has finally made its way to the Lone Star State.  So far the beetle has been found in only one location in Harrison County, next to Caddo Lake; but over the next few years it will continue to spread.  As it does, it will slowly change the face of our native forests as well as our urban tree landscape.

To prepare for the inevitable changes, Holly Jarvis with Texas A&M AgriLife Extension, has recently led an effort to develop an online training tool to learn about this powerful pest.

LearnOnline is a new Extension web resource for online courses.  The classes are free, and though not yet approved for pesticide applicator CEUs, they may qualify for advanced training hours for some Master volunteer programs.  Check with your local county Extension agent or Master Naturalist chapter officers for details.

Beyond getting official credit, the LearnOnline Emerald Ash Borer module is a great way to learn about, and prepare for, this new pest. To view the course, please go to You may be asked to set up and confirm your account via a link sent to your email address. Or, for the EAB course you can simply login as a Guest.

quarantine counties Aug 2016

Counties currently under quarantine (in yellow) for the Emerald ash borer in Arkansas, Louisiana and Texas.

To find the EAB course, click the category heading “Agriculture and Natural Resources”. A list of all courses in that category will come up. From there, click “Emerald Ash Borer”.  The course is approximately 25 minutes and includes a final quiz (optional if you want a certificate of completion).

Topics covered include “why should we care about EAB?”, “how to recognize the ash trees hosts of the beetles”, “recognizing EAB damage”, “EAB biology”, “who’s at risk?”, “reasons for hope and control options” for EAB.

Let’s get out there and “gird our loins” to fight the spread of this destructive pest.  If you have a favorite tree that’s an ash tree, you will benefit from knowing the battle plan.

New Zika publications

pregnant woman silhouette

Zika Precautions for Women is the latest of several new fact sheets designed to inform Texans about this new mosquito-borne disease.

I was asked a few weeks ago if the collective “we” (meaning the whole state of Texas) were going to be ready for Zika.  My answer was a cautious, “I think so”.  If we’re not, it at least it won’t be for lack of trying.

Zika is a much different disease than West Nile virus. It has different vectors, mosquitoes that prefer to feed on humans over any other animal (unlike WNV mosquitoes, which mostly feed on birds).  It is also very difficult to detect in wild mosquito populations.  The mosquitoes are more difficult to control with spray trucks, so responding to local cases is going to depend more on public cooperation.  Unlike WNV, it’s virtually undetectable in the blood supply, as there is no approved way to screen newly donated blood to see whether it has the Zika virus in it.

If Zika does make it into the country, it will also potentially affects more people.  Any family with members of childbearing age will need to be on high alert.

The CDC recently released its response plan for Zika.  It’s assumptions are sobering:

  • Travel-associated and sexually-transmitted cases will continue to occur and are likely to increase. (we just don’t know how much!)
  • Local transmission (spread) of Zika virus in US territories and affiliated Pacific Island countries is ongoing.
  • Neither vaccines nor proven clinical treatments are expected to be available to treat or prevent Zika virus infections before local transmission begins nationwide.
  • The ability for mosquito control efforts to reduce infection risks may be limited, as has been the case with similar viruses, such as dengue and chikungunya.

The entomology department, and especially my colleague Extension entomologist Dr. Sonja Swiger, has been busy in recent weeks trying to figure out how to best arm you with the best information on how to prepare for the “Summer of Zika”.  As part of the effort, some new fact sheets are now available to answer some of the more common Zika questions.

Quick fix for mosquitoes

This year my wife and I worked all spring to turn our backyard into a flowery paradise.  We installed drip irrigation, planted new plants (including a bunch of perennials for attracting bees and butterflies) and mulched everything against the coming drought of summer.

Now that summer’s here, however, the mosquitoes have decided that since everything’s so nice, they want to be in charge.  In fact I believe every mosquito on the block knows about our backyard, making it difficult to go outside for even a few minutes without repellent.

You see, clearing your own yard of mosquito breeding sites (as I have done) doesn’t guarantee a mosquito free yard.  So how do you take back your yard?  One quick fix that a lot of people are unaware of is the thermal fogger, available through most hardware and garden centers.


A thermal fogger in use.  Apply fogs in the early morning or evening, when wind is low and bees are less active.  Focus on thick foliage, shrubbery and tall grass where mosquitoes are most likely to hide.

Thermal foggers use heat from a propane burner or electricity, to heat a coil that turns certain oil-based insecticide formulations into a dense smoke of very small particles (10-25 microns–1/10 the width of a human hair).  The small size of these particles allows them to hang in the air long enough to kill flying mosquitoes.  The small size is also effective for penetrating foliage to kill mosquitoes resting in hidden locations.

Thermal fogging is easy to do, and relatively fast.  In my experience, I get several hours to a day or more’s relief from mosquito bites when I fog my backyard–plenty of time for that barbecue, birthday party or wedding reception.

The signature smoke from thermal foggers has its good and its bad points.  On the good side, you can see exactly where the insecticide goes and direct it where needed.  On the other hand, depending on the wind, the smoke may drift beyond your yard.  It’s a good idea to alert the neighbors before fogging your yard, or you might be seeing the fire truck pull up in your front yard.  Also, not all neighbors will be pleased by unexpected mosquito insecticide drifting into their backyard.

So what are the risks of fogging? Risks to humans and pets are very low with the common over-the-counter insecticides sold for fogger use.  But I find few good studies on the impacts of consumer fogging machines on beneficial insects.  I think it’s safe to say that there likely are some temporary impacts on the smaller beneficials like parasitoid wasps, and possibly the smaller bees.  But these insects are also typically highly mobile and should be replaced by other beneficial predators and pollinators quickly.  I believe it unlikely that larger butterflies and bees will be harmed by the low exposure rates used in mosquito fogging.  Although I am still assessing, I’ve not seen any noticeable impacts of occasional fogging on the larger insects I love to see in my garden.

Mark the term “occasional”.  Fogging for mosquitoes is not something I do regularly in my yard (though my vengeful side may want to do it more often).  I reserve my fogging ventures to once or twice a summer, and only when I’m expecting guests or planning a special outdoor event.  This way I can enjoy my pollinator and butterfly gardens and get my quick mosquito fix when I need it.

The rest of the time insect repellent works well.  And I am enjoying our newly planted gardens, despite the mosquitoes.

Reminder: Mosquito season and the risk of mosquito borne diseases kicks into high gear this month.  So don’t neglect the repellent and checking your backyard to make sure you’re not the neighborhood source of mosquitoes.

Turning the tide against ash borer?

Green ash
Tetrastichus planipennisi adult

Tetrastichus planipennisi is an obscure little wasp that specializes in finding and parasitizing the larvae of emerald ash borers.

On one hand, we’ve learned a lot about how to fight emerald ash borer with pesticides in the past 14 years since it was first discovered devouring ash forests in Michigan.  But we’re still learning how nature keeps EAB in its place in its native Asian home.  Insect parasites and predators are almost certainly the reason EAB is not a major pest on the other side of the globe.

If only we could put some of those same beneficial insects to work for us!  Then maybe we could slow the spread of EAB, and save our ashes at the same time.

That’s the idea behind research being reported this month by USDA Agricultural Research Service scientist Jian Duan and other researchers with the US Forest Service and the University of Massachusetts.  They looked at a tiny wasp, Tetrastichus planipennsi, that specializes in laying its eggs in the bodies of EAB larvae feeding under the bark of ash trees.

Over the course of the 7-year study the researchers saw a 90% decline in EAB larvae in infested trees caused by both native parasitoid wasps and by T. planipennsi.  They believe that once these fighting wasps are released in an area they will reduce the population growth of EAB and perhaps prevent outbreaks in newly infested areas–like Texas.

This will certainly be among the tools that the Texas Forest Service and others will be bringing into play as EAB makes its first tentative steps into our state.  In the meantime, don’t transport cut firewood when you’re out camping this summer, especially in the Caddo Lake region of east Texas.  And stay tuned for more news concerning the spread of this devastating insect.

Closer than you’ve ever been


mantispid by Levon BissPhotographer Levon Biss started out with portrait and sports photography, but got hooked on insects.  Now his extreme photographic skills have landed him a gig at the Oxford University’s Museum of Natural History.

Biss shoots his images through a microscope to create scenes that no human eye has seen before. That’s because, even for an entomologist with a very good microscope, it’s impossible to see a full insect, like the mantis fly image shown here, in complete focus all at once.

Biss achieves this by piecing together around 30 mosaic images, each of which might itself be a montage of 2-300 images shot at a slightly different focus point. Each picture in his exhibit at Oxford is comprised of between 8,000 and 10,000 images.

All this work allows Bing to create pieces of art that cover a canvas the size of a wall.  So if you can’t make it to Oxford University this summer, at least check out this video on Facebook to learn more about the process. Its worth the 5 minute watch time.

Emerald ash borer enters Texas

emerald ash borer damage
emerald ash borer damage

Dying roadside ash trees in another state. Ash trees are recognized by their opposite branching pattern and compound leaves. Photo by Leah Bauer.

If you’re a Texan and haven’t heard about an insect called the emerald ash borer, that’s about to change.  The emerald ash borer (EAB) is an invasive beetle that feeds almost exclusively on ash (Fraxinus spp.) and has been slowly spreading through the eastern and midwest states from Michigan where it was first discovered in 2002.

On May 23 the Texas Forest Service, along with the U.S. Forest Service, announced that four EAB beetles had been discovered on a trap in Harrison County, TX along the Louisiana border.  Although no infested trees have yet been discovered in Texas, these beetles signal a perhaps inevitable change in fortune all for Texas ash trees.

Last summer I visited Indiana where EAB has been active for several years.  The destruction was sobering.  Dead trees along highways, in parks, and in yards.  In fact you would be hard pressed in Indianapolis or Lafayette, where I visited, to find a single healthy ash unless it had been treated with a protective insecticide.

Emerald ash borer affected trees typically die two or three years after becoming infested. Native to Asia, nothing seems to be stopping the EAB, short of continual insecticide protection. The beetles have killed tens of millions of ash trees throughout the U.S., and currently 26 states are under quarantine restrictions for shipping of ash wood.

In the United States, 16 ash species are susceptible, and Texas is home to seven. According to TFS, ash trees make up less than 5 percent of rural Texas forests but are a larger portion of urban street and park trees. Texas A&M Forest Service is currently working with APHIS, the Texas Department of Agriculture, Texas A&M AgriLife Extension and the U.S. Forest Service, among other state and federal agencies, to implement a state response plan.

In a web conference this morning, state and federal officials sought to reassure the Texas timber industry that, at least initially, any impacts to forest products industry should be low. The TFS has established a new website where Texans can follow the progression of any invasion, and learn what steps that can be taken to protect your personal ash trees.

If you have an ash in your backyard there is little immediate threat unless you live in Harrison county, or an immediately adjacent county.  Experience with EAB in other parts of the country suggests that there is no need to treat your ash tree unless your home is within 10-15 miles of a known infestation, and that still has not occurred anywhere in Texas.

For more information about how to spot EAB damage see my earlier post at

And, by the way, if you’re looking for a nice shade tree to accommodate you in your retirement years, and you live in Texas, I wouldn’t choose any kind of ash.

2016 Entomology Specialist Training Announced

AgriLife Logo


One of the great opportunities offered to Master Naturalists and Master Gardener volunteers in Texas is a wide array of specialized training opportunities.  Entomology has its own version of this with Master Volunteer Entomology Specialist training.

MVES pin awarded to volunteers who successfully complete the class and volunteer hours.

MVES pin awarded to volunteers who successfully complete the class and volunteer hours.

Offered every year, MVES training is a multiday event designed to expand on normal entomology training every Master Volunteer receives during the internship program.  The curriculum is designed to appeal to both Master Gardener and Master Naturalist volunteers with an interest in insects.  Everyone who completes the course and volunteer hours on an entomology project receives a pin and status as an entomology specialist.

Class organizer for 2016 is Molly Keck, urban IPM program specialist for Bexar County, San Antonio. Molly does a great job and is an enthusiastic teacher.  She will be joined by an excellent slate of guest speakers talking about all things insect.  Presentations will cover Entomology 101, how to make an insect collection, blacklighting for insects, intro to beekeeping, Integrated Pest Management, beneficial insects, urban pests, veggie pests, landscape & ornamental insects, invasives, pollinators and much more!

Dates for 2016 are Monday September 26 (noon) – Thursday, September 29, 2016 (noon).  It will be hosted this year by the Bexar County Master Gardeners, and classes will be held at the Bexar County office and at Hardberger Park in San Antonio, TX.

To find out more about the program, and how you can register, go to   To see pictures from 2015 training, click here.


New fact sheet on indoor flies

dark-eyed fruit fly
fruit fly

Dark-eyed fruit flies are just one of several flies covered by the new publication.

Got flies? A new House and Landscape Series fact sheet will help you figure out what you have, and how to search out the source of the problem.

Indoor flies are opportunists.  Give them a place to breed, and they’ll be all over the place just like, well, flies.  Knowing where these breeding sites are is much easier when you know what kind of fly is driving you crazy.  Indoor Flies and Their Control (ENTO-050) reviews and provides pictures and descriptions of the most common small and larger indoor flies.

The publication covers both the smaller flies, like fruit flies, phorid flies, drain flies and fungus gnats, and the larger indoor flies like blow flies, house flies and soldier flies.  Each of these different kinds of flies have a preferred place to raise a family.  And by far the best way to rid your home or business of flies is to find and eliminate these breeding “hot-spots”.

When it comes to flies, we’ve all been trained to reach for the spray can.  But insecticide fogs and sprays provide, at best, only temporary control of indoor flies.  If you really want to be fly-free indoors, check out the new fact sheet.