Saturday, 30 April 2016

April’s Emeralds: the Cassida "Tortoise" leaf-beetles

The Tortoise beetles come out of their shells in April. They are well camouflaged and tortoise-like in appearance, with modified thorax and wing cases which are flattened at the margins to conceal their head and legs. An inexperienced eye could be forgiven for confusing them as a type of ladybird, if it does not miss them altogether. Once you have your eye tuned into them, they can be found in good numbers, blending in well with the green leaves that they bask and feed upon. There are twelve species present in the UK, most of which are green, but with a few exceptions - a couple of which are a stunning red and black (one of which - Pilemostoma fatuosa - is not one of the Cassida species, but it is closely related and still one of the "cassidine" tortoise beetles in the Cassidinae subfamily of Chrysomelidae leaf beetles).

Of the twelve UK species, personal experience suggests that the two most commonly seen species in the Newhaven area are Cassida rubiginosa and Cassida vibex, both of which can be found now basking on the leaves of knapweeds and thistles. C. rubiginosa, a species which has been used as a bio-control against thistles in Canada and New Zealand, is named after the small rust-coloured marks on its elytra (wing cases) behind the thorax, but C. vibex has a much more prominent red-brown longitudinal band tapering along its wing cases (vibex meaning a lash or streak).
Cassida rubiginosa mating pair
Cassida vibex basking on knapweed

There are several other species which are present in southern England and should be fairly easy to find on the Downs and along the Ouse Valley north of the Seahaven area. The Green Tortoise Beetle (Cassida viridis) is larger than the two species above and wholly green. It is found near water on dead-nettles (Lamiaceae) such as mints and gipsywort. The smaller, duller Cassida flaveola is found on pinks (Caryophyllaceae) including Stitchwort (Stellaria). The beautiful Cassida vittata with its distinctive longitudinal metallic green wing stripes feeds on many different plants in coastal areas, but is also an agricultural pest of beets and spinach. The similar Cassida nobilis, with its golden longitudinal bands, which feeds on goosefoots (Chenopodiaceae) is found inland from coastal areas.

The tortoise beetles feed on a number of plants, but mostly upon members of the daisy (Asteraceae) family including thistles, knapweeds and fleabane. They like a nice warm, sheltered spot out of the wind to bask on a leaf. If you choose a good location and if the weather is good, you could be rewarded with an emerald-encrusted experience - but careful searching is required because they really do blend in and they have an additional means of camouflage, which conjures a parallel image of the Cosmic Tortoise.

The cosmic tortoise is a mytheme (or creation myth) which commonly occurs in tribal mythology around the world. The tortoise goes by different names, such as the 'World Turtle', 'Divine Turtle' and, by the Native American tribes including the Iroquois and Lenape, as the 'Great Turtle'. Turtle and tortoise are interchangeable. The Chinese, typically, have to cut off the turtle's legs and use them to support the heavens after the mountain which had been doing the job - Mount Bizhou - was damaged. Art imitating life there, perhaps? In Hindu myth the turtle is known as Akupāra, which supports upon its back four elephants, which in turn support the world. Brewer's Dictionary of Phrase and Fable (15th Edition) gives the tortoise's name as Chukwa, which supports the elephant Maha-pudma, which in turn supports the world. An excellent account of this and other mythemes involving reptiles and amphibians is also given in the excellent and visually stunning book Eye of Newt and Toe of Frog, Adder's Fork and Lizard's Leg by Marty Crump (2015).

Akupāra supports the four elephants, which support the world

How does tortoise mythology warrant a digression from tortoise beetles? Tortoise beetles certainly do not support the world, via one or four elephants, upon their backs, but they do place something on their backs which further improves their camouflage: excrement! This is a fact which should not be concealed from the reader, but it is revealed to you in the hope that it will not turn you away from the potential for admiring these stunning little invertebrates. It is agreed that their 'faecal shield' poop-smearing behaviour is unpleasant, but the fact that so many are sporting the stuff demonstrates that it is a successful evolutionary adaptation, which of course is to be applauded. But it does also make them harder to find.

Cassida rubiginosa wearing a 'faecal shield'

How best to begin looking? One suggestion is to target specific plants in sheltered locations out of the wind on a warm day. I was rewarded with a dozen and a half Cassida rubiginosa and a few Cassida vibex sightings along a short stretch of path at Mount Pleasant the other day by looking for only a few minutes at knapweed plants, which are not yet in flower but still stand out distinctively from other plants amongst the downland grass. The beetles sit quite overtly on the knapweed leaves and are quite approachable. They play dead when disturbed and just drop to the ground. A single beetle on a leaf is often one of several on the same plant. The best way to get started, like many things in entomology, is to just get out there and enjoy the thrill of the hunt and to just enjoy being outside with the sun on your back away from the chill of the spring breeze and away from the mundane tasks of everyday life. Someone else is taking care of things while you're away. There's a tortoise supporting us all.

References:

Brewer's Dictionary of Phrase and Fable, 15th ed. 1995. Room, Adrian (Ed.). HarperCollins: London.

Eye of Newt and Toe of Frog, Adder's Fork and Lizard's Leg: The Lore and Mythology of Amphibians and Reptiles. 2015. Crum, Marty. University of Chicago Press: Chicago.

Cassida rubiginosa basking on knapweed
 




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