Caterpillar

May 03, 2022

I mentioned Zena’s predatory behavior when she had encountered a large caterpillar on the patio deck last week.  I felt bad as she first stomped it with her front paws and then ended up chewing it.  It must not have tasted very good as Zena spit it out almost immediately.  While this did not do much for the caterpillar she ate, it may help other caterpillars Zena finds if she remembers the first encounter.  When I went outside with Zena yesterday afternoon, I noticed the same type of caterpillar slowly working its way along the chain link fence that surrounds the patio.

When I looked online, I found the eastern tent caterpillar (Malacosoma americanum) is a species of moth in the family Lasiocampidae, the tent caterpillars or lappet moths.  It is univoltine, which means it produces one generation per year.  The tent caterpillar is a social species that forms communal nests in the branches of trees.  It is sometimes confused with the gypsy moth and the fall webworm, and may be erroneously referred to as a bagworm, which is the common name applied to unrelated caterpillars in the family Psychidae.  The caterpillars are hairy with areas of blue, white, black, and orange.  Tent caterpillars are among the most social of larvae.  The adult moth lays 200 to 300 eggs in a single batch in late spring or early summer and fully formed caterpillars are found in the eggs by three weeks.  The small caterpillars lie dormant until the following spring, when they emerge from their eggs just as the buds of the tree begin to develop.

Several of the trees at our house developed tents last fall indicative of the caterpillars.  When they hatch the small caterpillars stay with the tent until they finally venture out into the world to form cocoons and hatch into tent moths.  The tent caterpillars will vigorously thrash the anterior part of their bodies when they detect predators and parasitoids.  These bouts of thrashing can be initiated by a single caterpillar but move rapidly through the colony resulting in group displays of dozens of caterpillars.  The displays create a moving target for predators or species that would lay eggs on or in the body of the caterpillar.  The cherry leaves they chew are cyanogenic and the caterpillars will regurgitate cyanide-laden juices when disturbed.  We do not have any cherry trees in the patio area.  Perhaps the caterpillars on our deck are looking for some.

THOUGHTS:  The eastern tent caterpillar is toxic to horses and has been linked to mare reproductive loss syndrome.  Experimental studies have shown that when pregnant mares are fed eastern tent caterpillars, they abort, but it is unclear if this is from the caterpillar’s toxicity or for other reasons.  Zena is not a mare or old enough to be pregnant, so I am not worried.  All plants and animals have found ways to ensure their survival.  For some it is sheer numbers, for others camouflage, and then there are the bright colors often associated with toxicity.  Humans adapted similar ways to ensure our early survival but have since risen to the top of the food chain.  Now we use these mechanisms to protect us from each other.  Act for all.  Change is coming and it starts with you.