Only Your Best Interests At Heart

A caterpillar with a nematode infection. Image taken by Peggy Greb.

Here’s the problem: If you are a parasite and the animal you are parasitizing gets eaten then you get eaten too. This worm has a solution. It changes the color of its caterpillar host and makes it undesirable to would be predators, like robins. Normally a pale color, this caterpillar will turn pink-red. Find out more about this special little trick here.

Previously, not much has been found about parasites manipulating their hosts to avoid predation. In fact, the opposite has been seen-using chemical mind control to alter the host animal’s behavior to increase the likelihood of it being eaten so that the parasite might move on to the next stage of its life cycle. Or my personal favorite, the worms that live inside grasshoppers and then, once again using molecular mimicry and chemical mind control, compel them to leap to their watery death so that the parasite can live out the remainder of its life free swimming in a stream or river.

The Early Birds: American Robins

An American Robin with a mouth full of yummy worms. Image taken at the San Francisco Zoo.

This beautiful bird is a common one here in the United States. You can find them everywhere, but especially in parks or meadows. However they weren’t always so abundant here. These birds will actually roost together in winter in large groups of up to a quarter of a million birds. And like the passenger pigeon before them, these large roosts made hunting easy for those in the South who considered their meat a delicacy. However, as human numbers grew, their houses and buildings made great platforms for large robin nests and now they are protected under the US Migratory Bird Protection Act, so their range is expanding and they are doing quite well, although pesticides can still be a problem for them. These birds do eat insects as well as berries, but if they eat too many honeysuckle berries, they can get intoxicated!

Robins are usually the first to sing in the morning and they continue to sing through winter and fall. They are also the first to breed in a season (April-July) and will have 2-3 sets of young in a season. These guys are busy and have earned the well-deserved title of “the early birds,” which as you can see here…he he…gets the worms.

An American Robin collecting earthworms. Image taken at the San Francisco Zoo.

It is believed that robins find their worms by sight and some thrushes are known to stomp on the grass to mimic rain patterns in order to make their earthworm prey come to the surface for easier catching.

Our early birds also have to deal with predators, especially blue jays and snakes, and they do so by mobbing them, meaning attacking in groups. Some thrushes also defecate on their would be predators, leaving them to scurry off in a sticky, defeated mess. Win!