Tuesday, August 27, 2019

Weird Wild Neighbors: Yellow-necked Caterpillar

Today I bring you another weird wild neighbor that Erin and I encountered two days ago on Gillespie Point Trail...the yellow-necked caterpillar.

What makes the yellow-necked caterpillar weird? It has a strange defensive behavior to ward off would-be-predators. It was sitting on the middle of the trail outstretched in a seemingly relaxed posture when we first saw it, but when it realized we were standing directly over it the caterpillar threw its head back and raised its rear end as if it was doing some kind of back-bend yoga pose!

When it did this its six tiny legs vaguely resembled small thorns. I wonder, was that the point? If so, I thought to myself, what a bluff and what a gamble! It's great only if it works. If a foraging a bird or small mammal is confused or thinks its dealing with an insect having back spines for defense it might leave it alone; but if that defense strategy does not work the caterpillar has effectively exposed its most vulnerable parts to hungry predators!

I'd also like to share with you a note about how the introduction of a few invasive insect species have affected the population of the yellow-necked caterpillar:

"Throughout the Northeast this species and other Datana [its genus of caterpillars] appear to be declining. Compsilura, a tachinid parasitoid [a parasitic fly] introduced from Europe to control the Gypsy Moth, may be a factor in its demise. Over one ten-day period Compsilura attacked 79% of the fourth and fifth instar larva that Dylan Perry had set out in Massachusetts woodlands." (Caterpillars of Eastern North America. David L. Wagner. Princeton University Press; Princeton, NJ, 2005. Page 296)

It seems that introducing one non-native species to aid in the control of another non-native invasive species can have unintended negative consequences for our native species like the yellow-necked caterpillar and others, and impact the larger biological and ecological balance in unfortunate ways.

Perhaps the best thing we can do for our native wild neighbors and the spaces they call home is to work to prevent the introduction of non-native potentially invasive species rather then attempting to control or eliminate them after they have already become well-established.





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