The Miletinae - The Harvesters
A multi-tasking pair of Bigg's Brownie (Miletus biggsii biggsii) - mating & feeding amongst their protector ants
In the real corporate world, the title of this blog would probably not elicit much interest and excitement, other than offering a good read about yet another unfortunate company being swallowed up, or employees being thrust into a chasm of anxiety about their future.
A Bigg's Brownie (Miletus biggsii biggsii) feeding off what appears to be a "herd" of mealy bugs that are tended by their protector ants
In the world of Lepidoptera, however, the partnership between butterfly and ants is already a well-studied topic by entomologists. Myrmecophily, or the positive interspecies association between ants and butterflies (or rather, their caterpillars) has been widely studied. This symbiotic association occurs with some Lycaenidae caterpillars evolving specialised organs that exude honeydew in return for protection by the ants. These caterpillars then go about their daily business of feeding on the leaves of their host plants, whilst enjoying 'armed' guards' protection from predators.
However, there exists a subfamily within the Lycaenidae family - the Miletinae, that is unique in the sense that their caterpillars are predatory or "carnivorous" in the butterfly world. Whilst it is generally well-known that most caterpillars are "herbivorous" and generally feed on leaves, buds and flowers of plants, the Miletinae (or commonly referred to as the Harvesters) species' caterpillars feed on a variety of Homoptera like aphids, coccids, mealy bugs and one species even feeds on ants' larvae!
In Singapore, the Miletinae is represented by five genera - Allotinus, Logania, Spalgis, Miletus and Liphyra. Other than Liphyra, the other genera have caterpillars that feed mainly on a variety of Homoptera.
The aphids, coccids and mealy bugs, which form the principal diet of the caterpillars of the four genera mentioned, tend to feed on young shoots of various plants. These insects have adapted piercing mouth parts that pierce and suck the sap of plants - usually soft-stemmed ones. The Homoptera must suck large amounts of sap from the plant to get their nutrients. Much of the sap is a sugary fluid that cannot be digested. This extra liquid is passed through their body and excreted as "honeydew." Ants and other insects "farm" the Homoptera and collect honeydew for their own food. In return for their food, ants will protect the Homoptera that provide their colony with a food source.
In the field, observations have been made of the Miletinae adults feeding off the secretions of the aphids, mealy bugs and coccids. The butterflies do this brazenly, without any fear of being attacked, in the presence of the protective ants that are also 'milking' the aphids or mealy bugs of their honeydew.
Walking gingerly in a minefield of ants!
Besides feeding off the honeydew, the Miletinae also lay their eggs where the aphids and mealy bugs are present, and the caterpillars of these species feed on the aphids and mealy bug community.
It is interesting to note that the ants neither extract honeydew from, nor tend to the caterpillars in this case. They go about their business of tending to the aphids or mealy bugs, but leave the caterpillars alone - despite the caterpillars devouring their "herd"! Why then, don't the normally ferocious ants attack and kill the predatory caterpillars?
Miletinae caterpillars amongst their "sheep" which provides food as they grow
Researchers have postulated that the caterpillars (and even adult butterflies) have some kind of chemo-mimicry that render themselves 'invisible' to the ants. In other words, as far as the ants are concerned, the Miletinae adults and caterpillars are perceived as just another ant in the colony.
Hello? Are you my brother? An ant checks out a Lesser Darkie (Allotinus unicolor unicolor).
Therefore, although the caterpillars and adult butterflies of the Miletinae derive 'protection' from the ants, they give nothing back in return. On top of that, the adult butterflies partake of the honeydew that are secreted by the aphids and mealy bugs, and their caterpillars feed on the ants' source of food. Hence the "betrayal" part of the whole situation, where the ants have been hoodwinked into a win-lose relationship with the Miletinae.
An even more extreme situation occurs with the Moth Butterfly (Liphyra brassolis abbreviata). The caterpillar of this species feeds on the larvae of the Weaver Ant (Oecophylla smaragdina). It is interesting to note that the caterpillar feeds and grows inside the nest of the ants, and has evolved a clever way to escape the wrath of the ants when it ecloses. Our earlier blog article describes the Moth Butterfly.
A newly-eclosed Moth Butterfly (Liphyra brassolis abbreviata) whose caterpillar feeds on ant grub
This unique characteristic of the sub-family Miletinae in the butterfly world is amazing, and runs contrary to the conventional belief that all caterpillars are herbivorous and feed only on plant material. The adult butterflies of the five genera of the Miletinae found in Singapore are therefore very widespread, having little dependence on the location of host plants, as their "host" food is actually other living insects! Hence wherever there is a colony of aphids, coccids or mealy bugs, the adult butterflies of this sub-family will seek them out, for food for themselves as well as their young.
So do look out for these butterflies and special behaviour when you are out in the field!
Text by Khew SK ; Photos by Sunny Chir, James Foong, Federick Ho, Khew SK, Loke PF, Bobby Mun, Horace Tan & Tan Tze Siong
Well done!
ReplyDeleteWonderful post. Have always been amazed at this sort of evolution in Lepidopterans. Thanks a lot for the article and the stunning photographs!
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