Rearing the Large Blue Butterfly

REARING T H E LARGE BLUE BUTTERFLY, Maculinea arion L. The Large Blue is one of Britain's rarest indigenous butterflies, and although in years gone by it was found in other parts of the country, it is now confined to the Cotswolds and to the North Devon and Cornish coasts with, possibly, a few other localities. At the end of June and the beginning of July, eggs are laid by the females among the flowers of thyme, on which the larvae feed in their earlier stages. Immediately after their third moult, in August, the young larvae are only about 3 mm. long.

Until 1915, nothing was known of the habits of the larvae after this moult. It was known, however, that the young larvae were very attractive to ants which licked up small drops of clear fluid exuded from a gland on the lOth segment of the larva.

This symbiosis between ants and larvae is well known among other species of the " Blues ", the family Lycaenidae.

In May 1915, Dr. T . A. Chapman found a larva, about 11 mm. long, a few inches below the ground in the nest of the red ant Myrmica scabrinodis Nyl., and it was discovered that the Large Blue larvae ate the young brood of the ants. Further investigations showed that in August the young larvae left the thyme and crawled around on the ground tili they were found by the ants. The ants " m i l k e d " the larvae, caressing them with legs and antennae, so causing the larvae to exude the fluid from the " honey "-gland, the fluid being licked up avidly by the ants.

Some larvae were obserVed, after being " milked ", to swell up their first three segments, giving themselves a hunched-up appearance behind the head. VVhen a larva did this, the attendant ant would seize the larva in its jaws, taking hold between the third and fourth segments, and would carry off the little creature to its nest.

It was subsequently established that, once in the nest, the larvae become carnivorous, feeding on the ant brood and yielding their fluid in return. Pupation eventually takes place within the nest, and the butterflies, on emergence, crawl out into the open air where they rest on a Support tili their wings expand, dry and harden. These investigations led Captain E. B. Purefoy to try to rear the insect in captivity. He succeeded in doing this by keeping small nests of ants under walnut-shells, which were placed in tins surrounded by a " moat " of water.

DĂźring the last six years, I have been attempting to repeat Capt. Purefoy's success, largely with the object of obtaining photographs of the insect in all its stages. In addition to the

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REARING THE LARGE BLUE BUTTERFLY

walnut-shell method, various types of ant-observation-nests have been tried, and before myfirstexperiments were made I constructed a " Janet " type observation-nest. This was made of plaster-of-paris, the top being covered with glass so that the insects could easily be watched. It had several compartments which could be kept dark or light, as desired. A nest of the red ant, M. laevinodis, with plenty of brood and a few queens, w introduced so that they could settle down before Large Blue larvae were, in their turn, introduced later in the year.

The following is a short account of the results obtained : 1950. At the end of June, two female Large Blues were received from a friend who caught them in the Cotswolds.

They were enclosed with sprigs offloweringthyme and a number of ova were deposited, some among theflowersand a few on the surrounding glass vessel. When the resulting larvae had left the thyme, they were introduced into the " Janet " observationnest. One of the larvae kept close to the ant brood, but the others were more inclined to wander away into odd corners. The larvae were not seen to hunch their backs nor were any ants observed to lick the " honey ", although on one occasion a drop offluidwas seen to be exuded by one larva. After a few days, no Large Blue larvae remained, and it was assumed that they had been devoured by the ants, an action that in later experiments was seen actually to occur.

1951 - 52. In addition to the " Janet " nests, a few walnutshell nests, similar to those used by Capt. Purefoy, were made up and stocked with ants in May. At the end of July, several Large Blue larvae, from ova laid by Cotswold females, left the thyme. On 26th July, six larvae were placed in the daylight compartment of the " Janet " nest. Some were observed to be " milked " by ants and two were seen to be carried into an inner, dark compartment, but no hunching was noticed. Later in the day, all six larvae had been taken into the dark. On the following day, none of them could be found. More larvae were put into the daylight section ; several were picked up by ants and taken into the dark. One larvae was seen to be " milked " for a considerable time, and it hunched its back three times.

Each time, the attendant ant tried to carry away the larvae, but it managed this only at the third hunching. It was then observed that the larvae already in the dark were being eaten by the ants.

As a consequence, experiments with the " Janet " nest were discontinued and a number of larvae were introduced into the walnut-shell nests, four into one shell and two into another.

On llth August, three of these larvae were still surviving and they continued to grow slowly. At the end of October, the shells were covered over with earth and left for the winter. In J[anuary, 1952, the nests were examined ; two larvae were surviving, but

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REARING THE LARGE BLUE BUTTERFLY

in March there was only one left alive. At the beginning of June, this larVa, which had not grown at all since the winter, was transferred to a glass tube containing ant larvae but with no ants. The Large Blue larVa spun silk threads on the side of the glass, but did not eat any of the ant larvae. After a few days, it was returned to the shell nest, but it still did not grow and died at the beginning of July.

1953 - 54. In May, ants (M. laevinodis) were introduced into an old kitchen sink containing earth and stones to simulate more natural conditions. The sink was stood on pots that themselves were Standing in water so as to prevent the red ants from escaping and to prevent the entry of other species of ant. More ova of the Large Blue were obtained from females caught in North Devon, and four of the resulting larvae were introduced into the sink-nest and were left undisturbed. In the following summer, the sink was covered with netting, but no Large Blue butterflies ever emerged.

Shell nests were also used, as previously described, and in the spring of 1954 one larva was surviving and continued to grow, reaching fĂźll size in June. On 20th June it had spun up on the roof of the shell, preparatory to pupation. It did not pupate however, and eventually died.

1955 - 56. In July 1955, more ova were laid by females, this time from North Cornwall. One of the resulting larvae was placed in a Vertical type of Observation nest, but it was attacked and eaten by the ants. Twelve other larvae were introduced into shell nests and treated as in previous years. Three larvae survived the winter but only one started to feed on the ant brood in the spring. At first, the rate of growth was so slow that it did not seem as if the larva would survive. However, in June, it grew rapidly and on 5th July it had spun up on the roof of the shell. It pupated on 9th July, falling to the earth below in the process. It was pale yellow in colour and somewhat translucent. Later, it became darker and more opaque. The insect remained in the pupal stage so long, and the season was becoming so advanced, that it was feared that the experiment had failed once more ; but on the 4th August, 1956, the pupa turned very dark and the wing markings were faintly discernible under the skin of the pupa. On 7th August, a perfect female emerged.

T h u s was successfully concluded a series of experiments of immense interest. T h e many disappointments met with must be regarded as inevitable when attempts are made to rear a species of such an unusual life history.

S.

BEAUFOY.