Bustards, the largest flying birds, are ground-dwelling birds found in Africa, Europe, and Asia. There are 26 species in the family Otitidae, ranging in size from 16 to 60 inches. The Great Bustard (left) can weigh as much as 40 pounds while the smallest species, the Little Brown Bustard, weighs around 1.6 pounds. Bustards are omnivorous, feeding mainly on seeds and invertebrates. They have strong legs and big toes, pecking for food as they go. Most prefer to run or walk over flying. They have long broad wings with “fingered” wingtips, and striking patterns in flight. Many have interesting mating displays, such as inflating throat sacs or elevating elaborate feathered crests. The female lays three to five dark, speckled eggs in a scrape in the ground, and incubates them alone. Bustards are gregarious outside the breeding season, but are very wary and difficult to approach in the open habitats they prefer.
We’ve known for many years that a number of insects contain distasteful chemicals that deter predators from eating more than one of the insects. The case of the monarch butterfly larvae and Blue Jays is well known.
During the breeding season, males of the Great Bustard, Otis tarda, ingest large amounts of blister beetles, a black and red toxin-producing insect. Blister beetles are so called for their defensive secretion of a caustic agent, cantharidin, which causes burns and blisters on the skin and is poisonous if ingested. When handled roughly by a person or animal, the blister beetle breaks open a blood vessel on one of its legs to release the toxin. The color of the beetle is a warning to predators that trouble awaits them; this must be a successful strategy as there are 7500 species of blister beetles.
As reported in PLOS ONE “Especially during mating season, great bustards eat certain toxic species of blister beetles to prove how tough and healthy they are. Scientists have discovered that it’s not just bravado; the toxins from the beetles also kill parasites that live in the birds’ reproductive orifice known as the cloaca. The cloaca, which is also used for defecating, is then rigorously inspected by the female. The male’s white plumage is thought to make this examination easier, as the darker orifice stands out against the bright feathers. If the female deems him to be low enough in parasites thanks to all the poisonous beetles he’s been slugging down, the pair will mate.” There is also evidence that the consumption of canthardin is used to increase courtship display- it is, in other words, a sexual stimulant.
Cantharidin has been traditionally used by many cultures as an ointment for gout or arthritis, an aphrodisiac, or a wart remover. The sexual stimulant is sometimes called Spanish fly because the toxin is derived from a species of the same name.
Canthardin toxicity is apparently variable. The striped blister beetle is eaten by frogs who are immune to the toxin but retain it in their bodies; predators who eat the frogs, however, will be poisoned, including frog-leg eating humans. The Western Meadowlark, Scissor-tailed Flycatcher, and Eastern Bluebird, however, eat the striped blister beetle with impunity.