Why Are There So Many Dead Caterpillars?
TIOGA COUNTY, NY — An unusual chain of events is unfolding here at Entangled Acres. It’s a wonderful illustration of how everything connects at a global scale, so I will certainly write more about it later – but it’s so fascinating that I couldn’t wait to share this quick overview!
Towards the end of June, I noticed that my oak trees were covered in invasive Spongy Moth caterpillars. (USDA info link for Lymantria dispar) It was SO bad – hundreds of them climbing up every tree trunk, and in the canopy overhead. Frass (poop) was starting to rain down as they munched their way through the leaves.
I knew from past years that once they really get going, the sound of their droppings hitting the forest floor will be almost like a hailstorm. The tree branches would soon be bare, stripped of every single leaf. My tiny patch of forest would look completely dead by the end of July, and there was nothing I could do about it.
Luckily, healthy trees can usually recover from the damage. Unluckily, our local trees had already suffered from a bad late frost this Spring, followed by a drought. Most of my oaks already had visible signs of stress and damage from that frost; deformed and discolored leaves marred their majestic canopies. I was worried the combined stress might cause a massive die-off.
But, PLOT TWIST! Yesterday, when I tried to show someone else the insane scale of the infestation, the caterpillars had all mysteriously died. Every single caterpillar was totally limp or already decomposing into goop. After a bit of online research into possible causes, I found out that caterpillars are particularly vulnerable to wildfire smoke: https://www.futurity.org/haze-butterflies-caterpillars-2006532-2/
And ANOTHER plot twist: my oak trees’ trunks are now covered in slugs, as far up as I can see… It turns out that slugs will happily munch on dead caterpillars. We’ve had a few days of rain, so the trunks are soaked, and the slugs have cleared off every caterpillar carcass they could get to. The only untouched spot still sporting massive amounts of dead caterpillars is on the southern side of the trunk of an oak at the edge of the forest – a patch of tree bark that gets a lot of sun, and stayed too dry for the slugs to do their cleanup there.
I’m completely fascinated by all of this, and I can’t wait to write more and add pictures after the hectic holiday weekend is over. I’m sure that the effects of the wildfire smoke will continue to ripple throughout our environment for a very long time. And who knows how an explosion in the slug population, climbing into the canopy, will affect things?