The tropics are recognized as biodiversity hotspots (Gaston 2000) and this is particularly apparent in Lepidoptera, the order of insects that includes moths and butterflies. The warm temperatures of the tropics and constant food supply allow these insects to stay in one area and not have to migrate. The families have diversified so much that some, Hypeninae, solely live off of tears (Holloway et al. 2013) whereas others, Calpinae, have barbed proboscis to pierce the flesh of mammals and feed on blood (Zenker et al. 2011). Despite extensive speciation of Lepidoptera in the tropics, there are also predators always present, awaiting a tasty meal. To avoid being eaten and survive to another day these insects employ several different antipredator tactics. They use chemical defenses, mimic toxic species, camouflage, mimic other insects, and acoustic defenses. These defenses can be costly but are necessary to survival in the tropics, a beautiful yet dangerous place.
What better way to avoid being eaten than to taste awful? Several families of Lepidoptera use chemical defenses to be unpalatable and avoid predation. These substances can be sequestered as larva, procured from host plants, or due to de novo biosynthesis. The number of chemicals involved in these defenses are as diverse as the families which use them. Some of the chemicals which have presently been identified are: aristolochic acids, cardenolides, cyanogenic glycosides, glucosinolates, glycosidase inhibitors, iridoid glycosides, pyrrolizidine and tropane alkaloids, and pyrazines (Trigo 2000). Many of these butterflies and moths use aposematic coloration to advertise that they carry chemical defenses. Some also have urticating hairs which further irritate predators causing an intense burning sensation lasting hours. Other moths and butterflies will mimic these toxic families with similar colors and patterns but will not actually produce the chemical defense. Instead they rely upon predators learning from the toxic species to stay away.
Crypsis, the ability to avoid observation from predators, has been mastered by Lepidoptera. Where some animals may use colors and patterns to blend into their surroundings, some of these moths take camouflage a step further by disrupt the outline of their body to become inconspicuous. Some take form of a dead leaf or a twig while others mimic lichens. This mimicry of natural objects is called mimesis. Many species within the family Geometridea and subfamily Arctiinae (e.g. lichen moths) use this tactic.
The same subfamily Arctiinae also includes moths which mimic wasps. These moths completely change their morphology to create the illusion that they are stinging wasps. Even their movement patterns match those of the insects they are mimicking. At first glance one could easily be mistaken but by looking closely at their antenna, the moth’s true identity is revealed.
Arctiinae is an extremely diverse subfamily of moths which included 11,000 species worldwide. One of the most distinctive features of Arctiinae is their ability to use thoracic tympanal organs to detect ultrasonic calls from bats (Waters 2003) and to produce their own ultrasonic sounds with a specialized tymbal organ on their metathorax (Barber and Kawahara 2013). The males produce the sound as scales on their genital valve are moved dorsally and ventrally and grated against the inner margin of the last abdominal tergum. The females’ ultrasound production is also genitally based but has a different mechanism (Barber and Kawahara 2013). The function of these ultrasonic clicks are to jam bat sonar, startle naïve bats, and warn of unpalatability (Barber and Conner 2007).
Being a moth or butterfly in the tropics can be difficult but a number of tactics can be implemented to increase survival and fitness. Some insects use one of these strategies while others use a full arsenal. To begin to see the immense moth biodiversity that exists around you, you can hang a plain white sheet outside at night with a light shining on it. Soon the sheet will be crawling with life, mostly moths but some butterflies, beetles, and katydids as well. Each insect tells its own story of strife and success.
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Holloway JD, Barlow HS, Loong HK, Khen CV. 2013. Sweet or savoury? Adult feeding preference of Lepidoptera attracted to banana and prawn baits in the oriental tropics. The Raffles Bulletin of Zoology 29: 71-90.
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