Don’t let the name fool you. These guys are busy all year long!
Recently the WLBOTT Ag Extension Service (Go Waggies!) noticed an infestation of fall webworms in our 80-semi-demi-hemi-acre pecan orchard. We took immediate action, and it gave us an opportunity to explore WLBOTT Science!
The web is soft, silky, a bit sticky, and incredibly strong. I cut the limb down and cut thru the web to expose the little creatures. (Pro-tip for next time: don’t use your wife’s tupperware.) There appeared to be several separate life stages of the critters. I should note that these caterpillars are really, really gross.
After removing the sample, I further shredded the web and set it out near the garden. The birds and lizards had a big buffet.
The adult moths are elusive and exquisitely beautiful. I’ve only seen a few – they are almost pure white and soft looking.
The fall webworm (Hyphantria cunea) is a moth in the family Erebidae known principally for its larval stage, which creates the characteristic webbed nests on the tree limbs of a wide variety of hardwoods in the late summer and fall. It is considered a pest but does not harm otherwise healthy trees. It is well known to commercial tree services and arboriculturists.
Larva The caterpillars are highly variable in coloration, ranging from a pale yellow to dark grey, with yellow spots and long and short bristles. There are two cream stripes along the sides. The two races—one more common in the north, the other in the south—differ in head capsule coloration. The maximum length of larvae is 35 mm. Webs are progressively enlarged and much messier looking than those of tent caterpillars; also, webs from the fall webworm are concentrated to the tips of the branches, whereas the tent caterpillar webs are largely found in the unions. Larvae feed inside the tents until the late instars[1].
An adult specimen of Hyphantria cunea, commonly known as the fall webworm. By TampAGS, for AGS Media – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9419200
Very young larvae feed only on the upper surfaces of leaves; later, they consume whole leaves. The larval stage lasts about four to six weeks. Larvae are known to wiggle vigorously at periodic intervals in synchrony. How they synchronize these movements especially when distributed over a wide area has not been established.
Illustration of webworm (1917)
Thermoregulation Fall webworms experience behavioral thermoregulation. The fall webworms’ self-created web (which is where the fall webworms live) is able to trap heat. Due to this, the fall webworm (which is an ectotherm) is able to maintain a warm temperature of about 40-50 °C, which allows the larvae to grow and develop faster.
[ed. note: this is wild. The caterpillars have all kinds of tricks to regulate the temperature inside the web. Keep in mind that 50°C is 122°F.]
[1] Instars
An instar (from Latin īnstar ‘form, likeness’) is a developmental stage of arthropods, such as insects, which occurs between each moult (ecdysis) until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, changes in the number of body segments or head width.
Imperial moth (Eacles imperialis) development from egg to pupa, showing all the different instars By TheAlphaWolf – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=6418443
Eacles imperialis in Transylvania County, NC By NCBioTeacher – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=186438183
Eacles imperialis larva on Carya ovata in Alamance County, NC By NCBioTeacher – Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=186438282
That’s all that it says about the males. What exactly do they have on their calendar?
For anyone interested in creating an irresistible perfume, here’s the formula.
Sex pheromone The sex pheromone consists of the components (9Z,12Z)- 9,12-octadecadienal (I), (9Z,12Z,15Z)-9,12,15-octadecatrienal (II), cis-9,10-epoxy-(3Z,6Z)-3,6-henicosa- diene (III), and cis-9,10-epoxy-(3Z,6Z)-1,3,6-henicosatriene (IV).
The real mystery, though, is how entomologists discovered the 30–60 minute figure. Somewhere, a graduate student spent many evenings staring at moths with a clipboard, waiting for one of them to decide that romance had officially begun.
Elder G explains the mysteries of moth love:
Adult fall webworms (the moth stage) live only a short time and do not feed. Their main purpose is reproduction. Female moths release pheromones during a very specific period, usually around dusk. Males are highly responsive to these pheromones, but their responsiveness is tied to an internal circadian rhythm.
Researchers found that males are only strongly receptive to female pheromones during a relatively brief daily window, often about 30 to 60 minutes long. Outside that period, they may largely ignore the same signal. It’s as if their antennae are operating on “business hours.”
This is how the webworm guys spend the other 23 hours of their day:
Elder G manages their calendar:
7:22 PM Moths resting. 7:23 PM Moths active. 7:58 PM Moths extremely active. 8:01 PM Moths apparently remember they have an early meeting tomorrow.
The WLBOTT Agricultural Extension Service might summarize the entire reproductive strategy as:
“Fall Webworms: All the Romance of a Barry White album, compressed into the duration of a coffee break.”
WLBOTT Does Science
Using Elder DZ‘s USB microscope, we got some really gross pix of the fall webworm caterpillars.
I’m guessing that these are two different instars of the webworm.
Elder G really got into the humor of webworm mating rituals. For example:
Webworm Marriage Counseling
Counselor: When did the problems begin? Mrs. Webworm: He spends all day watching football. Mr. Webworm: In my defense, I’m only biologically motivated for 38 minutes. Counselor: That’s unusually candid.
Fall Webworm Pickup Lines
“Is that a pheromone plume, or are you just happy to see me?”
“I couldn’t help noticing your exceptional silk architecture.”
“You had me at volatile organic compound.”
Are They Edible?
Now we get to the question all our WLBOTT visitors are wondering: Are they edible?
Again, Elder G is the adult in the room:
The answer is one of those delightful combinations of “technically yes” and “WLBOTT should probably not make this a fundraising dinner.”
Fall webworm caterpillars are not known to be poisonous to humans, and there is no famous record of them being toxic. In principle, they are made of the same basic ingredients as many edible caterpillars consumed around the world: protein, fat, and a strong desire to eat your pecan leaves.
However, there is a several catch:
Nobody really eats them.
What Would They Taste Like?
Nobody seems to have published serious tasting notes.
My guess is that the tasting panel would produce descriptions such as:
Taster
Description
Sister Magdalena
“An occasion for prayer.”
Sally the Intern
“Needs more ranch dressing.”
Elder JA
“Could use hot sauce.”
Bev, the HR Director
“Absolutely not.”
WLBOTT Food Critic
“Hints of pecan leaf, regret, and administrative failure.”
