Scorpion beetles and lantern beetles

Everybody is familiar with the beetles or scarabs. They are so many that the great biologist Haldane said once that God, when he created the world, showed "an inordinate fondness for beetles". He created so many of them. There are about 600,000 described species, but probably there are 2 to 3 million species still alive, and mostly undescribed. Majority of unrecorded ones are among staphylinids, weevils, leaf-beetles, and several small genera, some not measuring more than 1 mm, others, the better known ones through collections and merchandises, measure several millimeters, centimetres, even 20 cm or more. Whether small or large, all of them need to be protected from extinction, including described and undescribed fauna. In the Permian, and later on after the Trias, probably they were hundreds of thousands, and probably non-existent at present. They are beetles in English, Käfer in German, bitter in Danish, and most of the languages have given them a common name, except in France. In France beetles are referred to as scarabees, carabes, bousiers, crache-sangs, taupins, coccinelles etc., there being no common name for the entire group of beetles. They are called « bilulus » in Zaire and « binatang » in Papua-New Guinea. In Zaire, during his youth, PJ got a nickname: "bwana biloulou", "Mister beetle", a memorable title. He was also Mr. Binatang in New Guinea, as Gressitt was, and all the beetle men there. Papuans and Congolese were good observers, and they always gave a nickname to the newcomers in their kingdom.

As for all insects, their body is wrapped in a hard shell, made of chitin, but in the beetles this shell is particularily strong and thick. Beetles are chiefly characterized by the first pair of wings, which are very tough and thick;

they are called elytra or wing covers, as they cover the membranous hind wings, carefully folded below the elytra in repose. Special rugosities on the wings and on the underside of the elytra help the folding process and keep the folded wings in place. Generally these insects are totally inoffensive to man, although some of them are provided with sharp and acute spines, which may prick the catcher.

Some beetles are poisonous and secrete a strong irritant, e.g. cantharidin by meloids or oedemerids. Some others are naturally poisonous due to presence of strong poisons in their body, like Melyridae (Choresine spp.). In New Guinea, they render birds or frogs, feeding on them, deadly poisonous. Batrachotoxins are neurotoxic steroidal alkaloids first isolated from a Colombian poison-dart frog (Phyllobate<s) and later found also in certain passerine birds of New Guinea. These frogs and birds do not produce the toxins de novo. Melyrids are also suspected in Colombia to be the source of the batrachotoxins in these vertebrates (Dumbacher et al, 2004). Poisonous frogs, birds and beetles have bright warning colours: orange and blue elytra in Choresine, bright orange belly in the birds (Pitohui and Ifrita).

Generally longhorned beetles (Family Cerambycidae), when they are grabbed, extend their antennae, which are sensitive and delicate receptor organs. Some neotropical cerambycids of the tribe Anisocerini and subfamily Lamiinae violently strike your hand with their antennae, if you seize them, and inflict serious wounds, which get infected rapidly in the tropics. They throw their antennae backward and upward, with a strong jerk, and then strike with the scorpion-like terminal joint. In fact the apical antennal segment in those beetles looks like a recurved scorpion sting. Fabricius gave this beetle the name Lamia scorpio. Common name for the beetle is scorpion beetle. All scorpion beetles belong to the subfamily Lamiinae of the Family Cerambycidae. The scorpion-beetles are big, nearly 3 cm long. They are crepuscular or nocturnal in their activity, clinging to rough bark covered logs during the day. They have rugose forms, and mostly have white scales over their body. They mimic lichens on the bark of the trees and are difficult to locate (Alvaranga Julio and Monne, 2001).

Scorpion beetles (Tribe Anisocerini, Subfamily Lamiinae) belong to several genera, including Onychocerus and Hoplitocerus, the former name meaning "horn with nails" and the latter "provided with horns". That the swollen terminal joint of the feeler encloses a poison gland has been suspected. But Smith (1884) has doubted it, and Costa-Lima (1955) has denied it. But on basis of a study of sections, Wandolleck (1896) inferred that there was such a gland. Zikan (in Costa Lima, loc. cit) considered the antennae as venomous, as well as Gahan (1899). For Kirby (in Wandolleck, 1896), the ending claw was used only to lay hold of surfaces. More careful studies are needed to confirm presence of a gland in the terminal antennal joint. It is really strange how books on beetles (Crowson, 1981; Paulian, 1988) and all encyclopedia of entomology have totally ignored these peculiar beetles. Miguel Monne reported (1982, pers. com.) that he had been many times attacked by scorpion beetles, around Rio-de-Janeiro, by using their antennae, when normally beetles use their mandibles or legs for inflicting wounds. The feeler wounds look like mosquito bites and they show gradual reddening. Hequet (1996) mentions and figures the Onychocerus in her book on Guyana longhorn bettles.

Among the Anisocerini, some, like Onychocerus scorpio, O. concentricus, O. aculeicornis, O. albitarsis, O. crassus, Cyclopeplus batesi, C. batesi, Hoplistocerus dives, H. dichrous, H. gemmatus have a more or less well defined scorpion sting-like ending antennae. Some more, among the many species found in the Neotropics, may also have such antennae, but other species of the same genera or of different genera, like Taurolema, Xylotribus, Acanthotritus, do not show sting-carrying feelers.

Many other beetles have long and sharp spines, but situated elsewhere and not on the terminal sting-like feeler joint. Femoral spines of certain species form efficient defensive weapons, as well as the thoracic spines of certain beetles. Femoral spines of some big moths, cephalic and thoracic horns of scarabaeids among beetles, and on many other organs have defensive value. Spines and pointed structures are also known on the antennae of some male Hymenoptera, but only in some Anisocerini, both sexes have the scorpion-like ending antennae.

Chemical defense exists among many cerambycid beetles. Toluene and o-cresol have been identified as the main volatile components in the defensive secretions of two species of Australian longhorn beetles, Stenocentrus ostricilla and Syllitus grammicus (Moore and Brown, 1971). The chemicals are produced in paired mandibular glands and emitted through pores on each side of the frons, via specialized frontal organs. So, it would not be surprising if antennae of some Anisocerini dispense chemical irritants.

After the scorpion-beetles let us have a quick look at the lantern-beetles, that is those which emanate light, e.g. glowworms (Lampyridae) and some click beetles (Elateridae). Oxygen, an enzyme called luciferase, and a compound called luciferin are involved in a complex chemical reaction to produce light, and adenosine triphosphate (ATP) provides energy for the reaction. The colour of the light produced may vary from red, yellow, blue, green to violet. The light thus produced is sometimes referred to as cold light, because of minimum heat production in the process. Fireflies convert 98% of the energy produced into light. Man is far away from achieving this result. With his bulbs and neon lights he transforms a much smaller percentage of energy into light, and the rest is lost as heat. Members of four or five beetle families are light producing. In Phengodes (Phengodidae), the photophores or light emanating organs of the anterior part of the body give out red light and the abdominal organs produce green. Bioluminescence is best known among fireflies, which are toxic, and that their luminosity has a warning (aposematic) function is a possible explanation (Lloyd and Gentry, in Resh and Carde, 2003). Light in fireflies like Photinus spp. is also a mating signal for the males. The code varies according to the species. Some predacious firefly females of the genus Photuris mimic the flash response of other species, attract males of those species and eat them. There is also a case of luminosity under water: the larvae of the firefly, Luciola, in India, Japan and Indonesia; they emit a blue light. In the Indo-Australian region, the males of Pteroptyx, which is a lampyrid, on trees, emit synchronized signals each half second. The exact meaning of this firework and the mechanism of this synchronisation have not been understood. Maybe it is for giving equal mating chance to all the females involved.

In fields of Central America, bright bi-coloured elaterids (Pyrophorus) fly very fast between the trees. The twin spots on their thorax produce a glow of such an intensity that there appears a long, golden red path of light during the flight (Klausnitzer, 1981). One of us (PJ) failed very often to capture them with a net in Nicaragua and Panama. It has luminous organs at the posterior angles of the pronotum and at the base of the abdomen.

These organs emit simultaneously red and yellow-green light. The Pyrophorus larvae are also luminescent and feed on scarab larvae. So strong is their luminescence that Humboldt is said to make with them a reading lamp. Missionaries during colonial times, as we are told, read their breviary with the help of the elaterids inside a glass bottle. Some Staphylinidae and Phengodidae are also luminous, even spiders in Burma. Many insects show light signals, often to capture preys in their webs, like Arachnocampa luminosa (Diptera, Family Mycetophilidae) in New Zealand caves and several Collembola. The ceiling of the caves in Waitomo, near Aukland, with millions of glowworms and their prey capturing threads, looks like a star-studded night sky. Several other Mycetophilidae are luminous in Australia and America. Light production, among beetles, which is not polarized and produces chlorophyllian assimilation, serves several functions: sex attraction, lighting of the soil when the insects land, trapping other insects, and warning about toxicity. However, there are some disadvantages too, like an easy location by predators such as bats.

It is difficult to explain why some longhorn beetles (Cerambycidae), having no close relationships with lampyrids, mimick the fireflies. They copy their external appearance and possess under the belly several segments clothed with whitish pubescence, in pure imitation of the luminous organ of the Lampyridae. Of course they are not real photophores; the resemblance is only in colouration, appearance and location of the hairy areas. These beetles have been given suggestive names, Alampyris. Alampyrisphotinoides, A. planipennis, A. mimetica are typical members of the genus. Early in the last century Bates mentioned their similarity with fireflies. Some Alampyris (A. nigra,, etc.), however do not show the pseudo-luminous spots. Alampyris is a Lamiinae. Many species of Alampyris are known from Mexico, Guatemala, Brasil, etc. Some species of Alampyris, like A. planipennis, have two yellow-green spots under the abdomen (segments 3-4), made of scales. It possible that they shine in ultra-violet radiation and be perceived radiating by potential predators.

Now there is a question. What is the reason of this similarity with lampyrids and why the copy of their photophore? The copy is nearly perfect. What is the use of these pseudo-luminous organs? Those cerambycids, of which the biology is a little known, seem entirely diurnal and the lampyrids are nocturnal. Why copy a nocturnal species, which certainly are very toxic? If they are active also during the night, this aspect could be a batesian protection against predators. They could this way copy the toxic and well protected lampyrids. Also, if the spot is shown in UV during the day, that could give the explanation. The Indo-Australian Pteroptyx offer extraordinary male nocturnal ballets, but no mimetic cerambycid is known there. Why is this phenomenon localized to Brazil and the countries around?

We have a nearly perfect case of mimicry among the Indo-Malaysian butterfly, Kallima, imitating a folded leaf, with false veins, false caterpillar bites, false fungus spots, and even a false petiole formed by the base of the hind wings, when resting on a branch. In that case the perfection could be understood. But why do S. American cerambycids go that far?

The uniform morphology of the photophores of the lampyrids has been inferred on the basis of their shape and their position. It is a possibility that these luminous organs act as do the eye-spot of so many Lepi-doptera. These spots of butterflies suggest the presence of head there. It is well known that among certain butterflies, like the Caligo, in Brazil, these spots are protective against birds. The butterfly turns over on its back, when it is about to be attacked by an approaching bird. The bird is surprised and stops a few seconds. In many cases the bird attacks the false head, suggested by the eye-spots, and the butterfly flies away with a small bit of wings missing. One often meets a butterfly with a bit of its hind wing torn and lost.

The explanation of the eye-spot is valid for the butterflies. Perhaps it is true also for the lampyrids and for the pseudo-lampyrids. But to have the end of the abdomen bitten away is not good for survival. Or as, said Rabaud, there is no explanation in the phenomenon and that it is pure chance, but as said one scientist "a non-adaptative character is a character not properly understood". We hope someone will understand and explain one day the Alampyris mystery.

— Fig. 29.1-29.2. Onychocerus crassus (Cerambycidae). Costa-Rica. The antenna is Showing, at the end, the scorpion tail. Among other species, the "tail" is more realistic (photo Jean-Michel Maes).

— Fig. 29.3. Onychocerus albitarsis from Brazil, showing in cross-section, longitudinally and transversally the "scorpion-tail" organ. The supposed venom orifices are said to be visible (after Wandolleck, 1896).

References

Alvarenga Julio, C. E. and Monné, M. A. 2001. Onychocerus Lepeletier and Audinet-Serville, 1830 (Coleoptera, Cerambycidae, Lamiinae, Anisocerini): especies novas e chave para identificaçao. Boletim du Museu Nacional, N. S. ,Rio de Janeiro, Brasil. Zoologia 443: 1-8.

Costa-Lima, A. M. da. 1955. Insetos do Brasil. 9. Escola Nacional de Agronomia Seria didactica 11: 201.

Crowson, R. A. 1981. The Biology of the Coleoptera. Academic Press, London.

Dumbacher, J. P., Wako, A., Derrickson, S. R., Samuelson, A., Spande, T. F. and Daly, J. W 2004. Melyrid beetles (Choresine): A putative source for the batrachtoxin alkaloids found in poison-dart frogs and toxic birds. PNAS 101 (45): 15857-15860.

Gahan, 1899. Onychocerus albitarsis. Proc. Ent. Soc. London.

Hequet, V 1996. Longicornes de Guyane. ORSTOM, Suilvolab, Cayenne, Guyana: 36 pp.

Klausnitzer, B. 1981. Beetles. Exeter Books, New York, USA.

Moore, B. P. and W V Brown. 1971. Chemical defence in Longhorn beetles of the genera Stenocentrus and Syllitus (Coleoptera: Cerambycidae). Journal of Australian Entomological Society 10: 230-232.

Paulian, R. 1988. Biologie des Coléoptères. Lechevalier-Masson, Paris.

Resh, V H. and Cardé, R. T. 2003. Encyclopedia of Insects. Academic PressElsevier Amsterdam, Holland: 115-120.

Smith, H. 1884. Antennae of a beetle used as defensive weapons. American Naturalist 18: 727-728.

Wandolleck, H. 1896. Den Fühler von Onychocerus albitarsis. Sitzb. Ges. Naturg. Fr.: Berlin: 51-56.

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