Do lions purr? And why are there no green mammals?

National Wildlife, August-Sept, 1995 by Doug Stewart

Other bug-bugging bugs are exactly what humans are looking for. In the southern United States, armies of fire ants have an inconvenient tendency to chew through electrical insulation (inside traffic-light poles, for example). Entomologists at the U.S. Department of Agriculture (USDA) are plotting to enlist a South American fly, Pseudoacton, to act as a mini Trojan horse. Female Pseudoacton lay their eggs inside fire ants. The larvae feed on the ants from the inside and finish up by decapitating their hosts.

Another internal parasite being tested by the USDA is a nematode worm that digs through the outer skin of aquatic mosquito larvae and makes itself at home. The worm even goes through several molts there, to its host's increasing detriment.

More subtle are the social parasites. These are animals that mimic the signals and behavior of high-status hosts - queen bees, for example - as a means of enslaving their oblivious underlings. One socially parasitic ant, Teleutomyrmex schneideri, is so adept at subjugating the colonies of another ant species that its own hunting and feeding organs have mostly disappeared, over time, along with its worker caste.

Explains psychologist Howard Topoff of Hunter College, "The parasitic Teleutomyrmex queen spends much of her life riding on the back of the host queen while being fed by the workers of the host species, an ant called Tetramorium caespitum."

And let's not forget hyperparasites: bugs that bug bugs that bug bugs - and so on. Some of the scenarios involving parasitic wasps suggest a Biblical genealogy ("Euryptoma beset Mesopolobus, which beset Toryus, which beset Syntomaspis, which beset Cynips, which started the trouble by besetting the gall of Cynipidae"). It's a bug-eat-bug world, all right. To quote the poet:

Big fleas have little fleas Upon their backs to bite 'em, And little fleas have lesser fleas, And so, ad infinitum.

How do birds find seeds they've hidden?

Apparently, even with thousands of hiding places to keep track of, birds try to memorize them all. "A black-capped chickadee encounters hundreds of seeds a day, maybe more," says Fernando Nottebohm, a biologist at Rockefeller University. "It stores from one-third to one-half of those seeds, usually singly, and it may do so over an area of 30 acres to a height of about 60 feet." A good sense of smell can't explain the bird's success at recovering what it hides, Nottebohm says, nor can random pecking. "It's very unlikely you'd hit the same spot again unless you remembered it."

So how can a little bird brain have such a fabulous memory? Nottebohm's research offers a clue. In a recent experiment, he measured a dramatic jump in the number of new cells in the black-capped chickadee hippocampus - the part of its brain that seems to be involved in spatial memory. The peak in the recruitment of new cells, which replace older ones that die, comes around October each year, just when the bird's seed-caching is at its most furious. He speculates that the new brain cells are better able to acquire new memories. Captive chickadees don't show the same cell growth. (Nor do humans, alas, regardless of their situation.) Moreover, says Nottebohm, "The hippocampus of birds that hide food is larger than that of birds that don't." He's quick to add that the evidence linking memory to these brain-cell changes is only circumstantial; he plans new experiments to study the connection more definitively.