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Cuckoos and caterpillars



All,

I had an interesting observation last Thursday evening. I have two
catalpa trees I planted in my backyard specifically to grow catalpa
sphinx caterpillars (the very best bream (bluegill) bait in the world).
These caterpillars are extremely gregarious and display aposematic
(warning) coloration in black, white and lime green. These traits
usually mean that insects are well protected from  predators by noxious
chemicals they pick up from their host plant, and, indeed, the
scientific literature suggests that these guys store lots of alkaloids
(the same chemical family that includes nicotine, caffeine and cocaine)
they acquire from the catalpa in their hemolymph ("blood" to an insect).
Thursday, I was out in the yard when I saw a yellow-billed cuckoo land
in one of the two trees. He casually peered around the tree, spotted  a
suitable caterpillar, snatched it, manipulated it then swallowed it. I
have never seen any other bird attempt to eat one of these caterpillars
although I have seen many birds of several species in the vicinity of
heavily infested trees, so I got my binocs out to see what the cuckoo
was doing. Under closer scrutiny, I saw that what he did was mash the
caterpillar rapidly from end to end with his bill; he then flicked his
head repeatedly from side to side, and I could see droplets of hemolymph
scattering away. In other words, it appears that he was processing the
insects to remove the noxious chemicals they contained in their
hemolymph. He then swallowed it and looked for the next victim.

Yellow-billed cuckoos are caterpillar specialists, and they are one of
the few species that routinely eat hairy caterpillars like webworms and
tent caterpillars. They often attempt to knock the hairs off these
species before eating them, so maybe this catalpa sphinx processing
behavior is an extension of the hair sweeping behavior.

Take care,

Clyde Sorenson
NCSU Dept. of Entomology
Clayton and Raleigh, NC
clyde_sorenson@ncsu.edu