Nearly one quarter of the worlds butterfly population have larvae that share associations with ants that range from being mutually beneficial to where ants become the main item on the caterpillar’s menu. The most recognizable are the Lycaenidae or the Gossamer-winged butterflies such as our harvesters, coppers, hairstreaks, and blues. In many cases these caterpillars and ants have a mutualistic relationship. The caterpillar feeds entirely on plants and has the ability to secrete a combination of sugars and amino acids called honeydew from a dorsal nectary organ on its back. Ants love the stuff so much that they turned it into a protection racket.

Normally the Lycaenidae caterpillars go about their business and don’t start serving lunch until they sense that there are ants nearby. Once the ants locate the caterpillar they drum on its back with their antennae and forelegs to start the flow of honeydew. Once they prime the pump they will then milk the larva for all its worth. In return for this delicious delicacy the ants will very aggressively fend off  any predators and parasites that may cause harm their meal ticket. To further safeguard their energy source they will even take the caterpillar into their nest to nurture it until adulthood.

So cool, all the little forest creatures should dancing in a big circle holding tarsi and claws singing Kumbaya, right?  Oh no so fast there Pilgrim there is a very, very dark side to the Ant B&B.

The Large Blue, Phengaris arion from the UK became extinct in 1979. Not to worry though because it has been reintroduced as part of a highly successful conservation project as was the Karner blue in the US but that is a different story for a different Tuesday.

But here’s the deal with Big Blue and it all starts and ends with Oregano. In the UK there is a species of ants called Myrmica. They truly love Oregano but for the plant the feeling is not so mutual. So once an army of Myrmica ants move in they take over the root system of the Oregano plant and in a defensive reaction the plant will produce a chemical agent called Carvacrol to ward off  the invaders. Unfortunately for the Oregano plant Myrmica ants are equipped with a set of genes that neutralize Carvacrol. Sensing that the first wave of Carvacrol was not strong enough the plant will double the dose in attempt to discourage the intruders.

Carvacrol also give Oregano its scent, one that gravid Large Blue females cannot seen to resist. The females will lay their eggs on the wild oregano plants where the young caterpillars will feed on the oregano flowers for about two weeks before dropping to the ground. At this point the caterpillar has the ability to produce a scent so similar to that of an ant grub that the ants will actually carry it back to their nest. The caterpillar can remain in the colony up to 11 months goring on grubs and getting fat. To encourage its minions to bring it even more grubs to feast on the caterpillar can imitate the sounds of their demanding Queen and the ants are easily fooled in serving the imposter another meal.

Hopefully the hungry, hungry caterpillar will eventually eat enough ant grubs that the colony will collapse and the Oregano will win out in the long run. The system seemed to work for a few centuries but unfortunately, as with many other butterflies, the eventual loss of habitat caused them to become extinct. But all was not lost. The Large Blue can once again be found in the UK but only because the population is the result from a starter stock from Sweden.

The Karner blue is currently being reintroduced in various locations in the US by the releasing captive livestock….But aren’t many the butterfly scientist telling breeders that they are environmental terrorist? Then again I’ll be the first to admit that I ain’t the sharpest bulb in the deck but if you can repopulate by breeding and you have an eager army of breeders out there…… Can you say grants?