The Human Botfly: You Take Your Lumps!

 

Dermatobia hominis, take a bow!

Anyone who can stand my articles know I am immune to creepy-crawlies, at least semantically. These little insects and arachnids are certainly interesting and it behoves us to know something about them in order to be on our guards when in their territory.

Tonight’s protagonist is one you won’t meet often in the chill of the temperate countries, such as Europe and most of the United States - although many creatures are spreading these days, hiding in cargo on ships and international flights. Britain, for example, has had a few surprised folk turning up in the emergency wards having been bitten by an “unusual” spider which turned out to be one of the world’s most dangerous arachnids, the Brazilian Wandering Spider, which had far exceeded it’s usual wandering habits. So far, no one has died from a globe-trotting venomous creature in the UK anyway; it’s probably only a matter of time.

But tonight’s “nastie,” the Human Botfly, prefers the tropics with their heat and high rainfall. They are in Mexico, and all points south, which means there’s little stopping them from infiltering the USA; the alien fence can’t even stop 200 pound wetbacks; the botfly will merely chuckle as it flies over it and insouciantly drops a few maggots into one of the ‘migra. Specimens of the 150 known species have also been found in Canada, Hungary, New Zealand and parts of Africa - whether these are of the human botfly variety I am not sure (this is the only member of the species which preys on man).

But botflys are different than most of the blood-suckers we have looked at the past several months. They don’t actually come near us nor the other large animals their larvae preys upon. This clever little cuckoo of the insect world has an accomplice, albeit an unwilling one.

When the female botfly is ready to lay its large eggs, it uses its speed and strong flight to capture a female mosquito. A female mozzie, because the males never bite humans, only Mrs Mosquito; the males feed on plant sap.

Once the botfly has a mozzie in its power, it lays its 10 to 30 sticky eggs on the mosquito where they become attached. The mosquito does what female mozzie do, finds a human or animal blood meal. As it pushed its proboscis into the flesh, some or all of the botfly eggs become detached, quickly release the larvae, one of which enters through the hole made by the mosquito. This remains near the entrance hole which it need for oxygen and begins feeding on the host’s living tissues. The larvae soon begins to grow and the area quickly becomes irritated from its saliva and excreta as well as from the host’s natural defences. A hard lump soon becomes apparent; if the botfly larvae is untouched, as it often is in cattle and other wild animals, it will stay for more than three months before enlarging the entrance hole and crawling out to drop to the ground and move on to pupate in the soil.. In humans, the larvae is usually removed in a minor, out-patient operation.

Botflies have also been reported using houseflies as vectors to carry their eggs/maggots. One variant, the Warble Fly, which commonly preys on caribou and reindeer has its maggots removed when northern natives butcher the animals and they are eaten as a delicacy: rather like wichetty grubs in Oz, or the gusanos de maguay in Mexico.

Botfly eggs and larvae can also be eaten by the host animal and reside in the gut until they are mature and passed in the animal’s excreta. This is particularly disturbing in domestic horses (see below).

Another specialist botfly concentrates on small mammals, such as rats, generally not doing enough damage to kill the host, but, in some cases, eating the testes and/or ovaries! I am indifferent to rats; rather admire them if anything, but I pity those picked on by the botflies.

Notes for Horse Lovers

Botflies can be a particular menace to equestrian caretakers as they lay their eggs in difficult to clean places like the cannon bone and must be removed before horses locate them and lick them off, passing them into the intestinal tract. They look like tiny drops of yellow paint. Wikipedia has some info on this.