Friday Cat-erpillar Blogging is back.
The caterpillar most associated with milkweed is the Monarch Butterfly Caterpillar. However, other caterpillars can also be found on milkweed. This includes the gregarious, Euchaetes egle, the Milkweed Tiger Moth. Like the Monarch caterpillar, the Milkweed Tiger Moth caterpillar sequesters toxins from the milkweed plant to defend against predators. Day flying butterflies can defend against bird attacks by advertising their toxicity with bright orange and black warning colors. The Milkweed Tiger Moth has bright orange warning colors on its body to warn day flying predators. However, the moth flies at night and can be attacked by bats who cannot see the warning colors. To advertise their unpalatability to bats, the moths use their sound organ to make ultrasonic clicks that are audible to bats. The “trash talking” by the moths warns bats to keep a safe distance. Nickolay I. Hristov and William E. Conner discuss this behavior in a NATURWISSENSCHAFTEN paper(Volume 92, Number 4, 164-169, DOI: 10.1007/s00114-005-0611-7).
Unlike the Monarch that lays eggs singly and caterpillars are solitary, the Milkweed Tiger Moth lays eggs in clusters and the larvae and pupae are gregarious. As you can clearly see from the pictures below, the Milkweed Tiger Moth undergoes several changes in its appearance during its development. The newly hatched first instar caterpillars have no tufts at all. The second instar caterpillars have spines but not tufts. Third and later instar larvae have full blown tufts. The older larvae sport tufts of hairs that advertise their bad taste. The tufts offer potential predators a bad tasting mouthful of hair that causes minimal damage to the caterpillar. If one caterpillar is attacked by a naive predator, the rest will be spared after the predator becomes sick from the toxins.
The pupae are fuzzy balls covered with spines. The spines can offer protection against predators such as ants and some parasitoids.
Of course, the moths look nothing at all like the earlier life stages. This exemplifies some of the problems with identification of insect larvae. If I had not grouped these together, would you be able to make a connection between a first instar larva and a third instar larva based on appearance? This is one of the reasons why entomologists are working on DNA markers. The DNA of the caterpillar is the same as in the pupa and adult. The DNA markers can allow us to connect different stages of the same insect that may look nothing alike.