Fall Cankerworms - Alsophila pometaria
Do Inchworms like to party? Absolutely! Especially if they have other Inchworms around them, and there’s quite a few here! These are the partygoers that eat all the snacks without heed.
Truthfully speaking, these Caterpillars are in fact Inchworms as they belong to the family Geometridae, or Geometrid Moths. They move in a looping motion, pulling their body forward and creating an arch along their back as they do so. Then they straighten out and move forward again, inching their way to their destination. If you look closely, a few partygoers here are in the process of arching their way across this wooden observation fence. The adult Moths conversely are more known for the wave-like patterns that travel across their wings. We’ll return to the adults shortly; for now, let’s focus on the aggregation of Cankerworms in the forest. How they all wound up on the wooden fence is anyone’s guess, especially since it is devoid of leaves to defoliate. It’s possible they may have hatched on the fence itself, being placed their by a female Fall Cankerworm Moth thinking it was some type of hardwood tree. However, it’s more likely that these individuals are descending to pupate. You see, based on their appearance, they’ve been active for some time now. Upon hatching, Cankerworms begin their lives colored green, gradually darkening with each molt as they grow bigger, just as these have.
They may darken to black from instar to instar, but while they wriggle around they never lose the white bands that trail from head to toe. The band isn’t as visible when green, and neither are the Caterpillars for that matter. They use their green colors to their advantage by straightening their body and mimicking twigs if they feel a threat nearby as they feast at their tree. They’re well anchored thanks to their rear prolegs, so maintaining this posture isn’t an issue. After eating, defoliating, and molting, these Caterpillars find their way to the soil and pupate. The forest finds some peace in the meantime as the voraciousness of these Caterpillars has the potential to be devastating if left unchecked by their predators (both from birds and insects). As the seasons pass and autumn arrives, it is found they these Cankerworms don’t overwinter as pupae. The emerge as grey-colored Moths and seek out the best trees to place eggs and ready the next generation of Caterpillars for the winter. It may sound straightforward, but the female Cankerworms emerge without wings (my sentiments on that were covered in a Bagworm post), making location-seeking much more urgent! Next time you’re in a forested area where these wrigglers can be found, return in the autumn months and look for stout, grey, wide-bodied wingless Moths (grey-winged, male Moths may be nearby). It’s a strange sight, but it’s just another part of this insect’s journey. And being wingless does have some advantages: males come to you, less energy burned on flight and the potential of parthenogenesis (reported in some populations).
Picture was taken on June 10, 2017 at the Royal Botanical Gardens with a Samsung Galaxy S4.
