Nature is full of impostors. Pretending to be something you are not is a strategy that works well for many species. Classic examples of this in the insect world are the numerous files and moths that impersonate stinging bees. This type of trickery is called Batesian mimicry (after Henry Walter Bates, the English naturalist that came up with the concept). Many predators (along with kids and non-entomologist adults) are generally fooled by this display. It’s natural that, after being stung by a bee, people generally want to avoid being tagged again. Sometimes this reaction is extreme and the mere sight of a wasp-shaped, black and yellow-colored insect can send someone into a panic – even if the insect is unable to sting.
A couple of months ago we were visiting my wife’s grandmother who has a sprawling farm down near Fayetteville. The area right around her house is filled with beautiful, well-developed flower beds that were buzzing with pollinators at the height of summer. I noticed that one of the species that was fluttering around the flowers was a moth (probably Hemaris diffinis) which put on a very convincing impersonation of a bumble bee. It was so convincing that the kids were not willing to get close enough to verify that it was indeed a moth. We also saw a couple of flies that were also successful bee mimics. In fact there are numerous species of flies, non-stinging bees and at least one beetle that have evolved this same trick of looking like a stinging bee or wasp.
Aggressive mimicry is essentially the opposite of Batesian mimicry and a tactic whereby some plant or animal appears to be something harmless or attractive in order to get close to their prey. One of my favorite examples of this from the insect world are the femme fatale fireflies (Photuris spp.) discovered by Dr. Jim Lloyd from the University of Florida. The flashes of light from all species of fireflies that fill a field at dusk are the signals they use to defend territory and find mates. The pattern and duration of the signals are unique for each species of firefly and only the right timing and pattern of blinks will do. Signals that don’t conform to these specifications fail to “turn on” the right mates. But the females of some Photuris species have evolved the ability to mimic the signals of females from a different genus (Photinus). This trick lures in male Photinus fireflies that have the impression they are about to get lucky. Much to their chagrin, the femmes fatales then capture the unsuspecting males and turn them into a meal.
Recently I’ve been working on an ant-tended aphid system wherein an aggressive mimic resides. The ants tend and protect the aphids from predators and parasites in return for honeydew (a carbohydrate rich substance exuded by the aphids that the ants eat). It’s akin to the relationship between humans and dairy cows where cattle are cared for in exchange for producing milk. However, in some of the aphid colonies I’ve found hover fly larvae (Syrphidae) that the ants treat in much the same way they do the aphids. These hover fly larvae are voracious predators of aphids and will consume several of them a day. But the ants don’t recognize it as a threat to their aphid herd and will protect and relocate hover fly larvae the same way they do the aphids. In all likelihood the fly larvae have acquired the same “scent” as the aphids through evolution or by feeding on them. In either case, it’s the proverbial wolf in sheep’s clothing.
Last week, a paper was published that describes a new type of mimicry that is used by an orchid to attract pollinators. Blossoms of the orchid Epipactis veratrifolia produce odors that mimic the alarm pheromone of several aphid species. Females of several species of hover fly use aphid alarm pheromones to find and select locations for laying their eggs. The larvae can then hatch out and just start feeding. While larval hover flies are highly-adept at preying on aphids, fast and far-flying adult hover flies are well-designed for pollination. By luring in these female flies that are looking for a place to lay their eggs, the orchids get the flies to pull double duty. The adult flies will collect pollen on their bodies as they search the interior of the orchid blossom before carrying this pollen to the next flower they visit. The female hover flies also leave behind their eggs which hatch into hungry larvae that patrol the orchid and feed on aphids and other small, soft-bodies insects that attack the plant. It’s a brilliant adaptation.
Orchids, many of which don’t produce nectar, are notorious for luring in pollinators using other tactics, like deception and mimicry. Some species (like those in the genus Ophrys) have flower structures and odors that mimic sexual cues. They have evolved to trick male insects into having sex with a fake “partner” while it gets covered in pollen. There are others, like Bulbophyllum phalaenopsis, that look and smell like decomposing flesh in order to bring in flies that are attracted to carrion. These plants have trap-like mechanisms that force the flies to get covered in the plant’s pollen before being released to carry it on to the next flower. However, the case of Epipactis veratrifolia, this orchid appears to be the first known example of a flowering plant attracting pollinators using the scent of live prey.