Thursday 19 June 2014

Cicadas Say Summer

For many people, especially in the southern half of France, the sound of cicadas buzzing in the trees is the sound of summer, and there is a saying il ne fait pas bon travailler quand la cigale chante ('it's no good working when the cicada is singing'). Even in the initially pathetic excuse for a summer that we had in 2013, the cicadas emerged on time in late June and zzzzzzzzed away. This year's summer has been fairly iffy so far, but yesterday I heard my first cicada, right on cue. During the warmer months I often hear them in the orchard, accompanied by the Field Crickets Gryllus campestris, but whereas I see the crickets every day sitting in the entrances to their burrows in the potager, the cicadas remain invisible up in the trees.

A female Tibicina haematodes (la Cigale rouge in French) photographed on a redcurrant bush in late June last year in a friend's garden in le Grand Pressigny. All the photos are the same species (and probably the same individual). This species is large, about 30 mm long.
Like so many creatures today though their numbers are in serious decline, especially in the south, where habitat loss due to vineyards being planted on large areas of the native garrigue is the main cause. There are about 20 species present in France, but only 2 or 3 are large, noisy and abundant. Like other true bugs, they suck sap from plants through a hypodermic needle like mouthpart. They are incapable of jumping, but can sit for hours completely still and camouflaged, their wings folded over their body pitched roof fashion. Only the males 'sing', producing the sound from an unique and elaborate system of 'cymbals' at the base of the abdomen. The males contract and release muscles connected to the 'cymbals' 300 - 900 times a second in order to produce the sound. To amplify the sound, their intestinal organs are pushed towards the tip of their abdomen, leaving most of their abdomen hollow and acting as a resonator. Each species has a different sound or pattern of buzzing. 
Their life cycle includes adults which can fly and nymphs which live underground. Once emerged as adults they have 2 - 3 weeks to live. In contrast, their life underground is of at least 2 years duration. Adults and larvae look more or less alike, with robust digging front legs and bristley faces. Since they are no use underground the wings remain vestigule and 'under wraps' until the adults emerge. The adults have very good sight, but the larvae are blind, although the eyes are there, behind a protective cuticle dome.

Females lay eggs inside plant stems or under bark. The larvae hatch as tiny things barely 1.5 mm long and head for the ground to bury themselves. Over the next couple of years they grow, moulting periodically as they outgrow their exoskeletons. They burrow through the ground looking for vegetable material to eat, their front legs excavating using their built in pick and shovel arrangement and their back legs pushing. They identify their surroundings using their facial bristles. They prefer dry soil, but when it is too dry and hard to dig they pee on it to moisten it and make digging easier.
After their 5th moult they spend 8 - 10 months in a sort of suspended animation, then another month preparing to metamorphise, changing from white to brown and green and positioning themselves vertically just a few millimetres below the surface of the soil. When ready to emerge as adults the nymph climbs above ground a short distance to split open the exuviae down the back. They are very vulnerable to predation by ants and wasps at this moment. After a few hours their exoskeleton has hardened and their wings pumped up and useable. Now they can fly to a nearby branch, sing and take their first meal of sap.
The males 'sing' to attract the females. Both sexes have 'ears' on the underside of their abdomen, very sensitive to vibrations and acting like sound mirrors. Once they have mated, the female will lay 30 - 50 eggs by inserting the very hard tip of her abdomen into a plant stem and depositing an egg.

Source: Biologie et Comportement des Cigales de France, M. Boulard, OPIE, 1988.
French Expression: En déplacement = on a business trip. I learnt this expression when one of our winemakers used it to explain why they would not be available one day. Now I use it when I explain to our laitiere (milk lady) that we will be away with clients so I don't want her to leave any milk.


Tim said...

What a fascinating life cycle! I love the sound of cicadas - it says "sun" to me. And those church-window wings are beautiful. P.

chm said...

Your photos are absolutely magnificent.

In the states we have annual Cicadas, but also 13-year and 17-year Cicadas, which means the nymphs spend all that time underground until, like Sleeping Beauty, millions of them emerge as adults, regular as a clockwork.

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