Dracula ants featured in the Brisbane Times recently, under the headline "Aussie ant crowned fastest in the animal kingdom". The article further explained that "dracula ants get their name from their strange desire to suck the blood of their children".
Of course, there's more to this story, and it's actually more fascinating than salacious.
Dracula ants in the genus Mystrium occur from Madagascar and central Africa, through south-east Asia to Australia. Most are Madagascan, with only a few species elsewhere in the range. One species, M. camillae, the subject of the Brisbane Times article, is native from Australia's Top End through south-east Asia to Malaysia.
Both the genus and the ant subfamily to which it belongs (subfamily Amblyoponinae) are relatively small, comprising only a handful of the more than 20,000 known species of ants, and are regarded as "primitive" ants.
The Brisbane Times article comes from this paper in the journal Royal Society Open Science, which describes a study by taxonomist Fred Larabee and colleagues from the National Museum of Natural History in Washington DC. The scientists were interested in dracula ants because of their very unusual jaws, which they use in an even more unusual way.
All ants have powerful jaws (mandibles) used for grasping and carrying prey and for defense. In almost all species, the jaws open and close by muscle power, with the speed and strength of closing limited by the speed and strength of the jaw muscles.
Dracula ants use their jaws differently. At rest, the tips of their long jaws touch each other and "lock" together". When the ant tightens its jaw muscles, the tips remained locked, with the jaws storing the muscle energy like a spring. Eventually, the force at the tips overcomes the locking mechanism and the jaws spring shut very rapidly and with great force.
The mechanism is analogous to the way we snap our fingers - with the tips of finger and thumb pressed firmly together, we use our muscles to progressively add tension until finally they snap apart, releasing the stored energy in a short burst, faster than the muscles could do acting directly.
Dracula ants use their snap-jaws to stun their prey (and perhaps also to escape from danger - pressing the jaws against the ground and snapping them throws the ant backwards out of harm's way). Once stunned and killed, the jaws are used in the normal way to dismember and carry their food.
The scientists used super-fast video microscopy to show that the snapping jaws of Mystrium camillae is the fastest biological action yet recorded, at 90 m/s. To put this into context, the snap movement is one thousand times shorter than the snap of a human finger and five thousand times shorter than the blink of an eye. This is substantially faster than any other measured organism, including termites (some of which also have a snap-jaw mechanism) and mantis shrimps.
Dracula ants also have what many would think is a very odd habit. The queens in larger colonies feed exclusively on the 'blood' (haemolymph) of their own larvae. Even when prey items are available, larval haemolymph is their only food. The queens gently stroke then pick up a larva, carefully piercing its skin with the tips of their jaws and sucking the drop of haemolymph that bleeds out. Feeding like this is not particularly harmful to the larvae, although it does slow down their development. This paper by Japanese entomologist Keiichi Masuko provides careful observations of haemolymph feeding in the Japanese dracula ant Amblyopone sylvestrii.
Why do they do this? There may be several reasons. Unlike in more highly evolved social ants, dracula ant workers don't feed their queens or each other by regurgitating food from their crops. While captured prey items may be brought back to the nest, ants feed on them individually rather than sharing via regurgitation.
They do however feed the larvae in this way. So in one sense the queens are being fed, but via the larvae. Even when prey items are readily available, the queens will not feed on them, perhaps because digesting larval blood is more energy-efficient, allowing the queen to focus on her one critical task, laying eggs.
Most dracula ants are specialist feeders, foraging underground where they capture burrowing centipedes. Centipede capture is relatively infrequent, so colonies often go for long periods without food. In this boom-and-bust situation, the larvae are used as a food reservoir for the colony, storing nutrients after a kill and being drawn upon, particularly by the egg-laying queen, during famines.
So far from being evil and destructive blood-suckers of their own children, dracula ants have evolved a sophisticated and efficient mechanism to support their lifecycle and ensure their survival.
Such is life.
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