The caterpillar is of a dull pale greenish colour, with numerous black speckles; three whitish lines on the back, the central one greenish tinged and broader than the others, which are interrupted on each ring by a yellow spot; between the lines is a series of black dots, one on the outer edge of each ring; hairs, from greenish warts, white and short; head, black, dotted with white. It feeds on bird's-foot trefoil (Lotus corniculatus), and other trefoils and clovers: August to May. Sometimes the caterpillars do not complete growth until they have passed two winters in hibernation. The cocoon, which is yellow or yellowish white, has been found on a grass stem, but
it is generally placed so low down among herbage that it seems to be rarely detected.
The moth is out in June and early July.
As previously stated the only part of Britain that the species inhabits is the New Forest, Hampshire. Here it was first met with in Stubby Copse, about 1869, but was apparently not distinguished from Z. trifolii until 1872. It is now less frequent in its old haunt than formerly, although it still occurs there; in other spots around, I believe, it is not uncommon in some years.
Some authorities refer this species to viciæ, Schranck.
Five-spot Burnet (Zygæna trifolii).
Four specimens of this species are portrayed on Plate [146]. In the typical form (Figs. 7 ♂, 8 ♀) the central pair of crimson spots are united and often form a large blotch; ab. orobi, Hübner (Figs. 6 ♂, 9 ♀), has the spots placed well apart. Other more or less frequent aberrations are depicted by Mr. Horace Knight on Plate [148] where Fig. 2 represents ab. glycirrhizæ, Hübner (spots 3, 4, and 5 united); Fig. 3, ab. basalis, Selys (spots 3 and 4 united with the basal pair); and Fig. 4, ab. minoides, Selys (all the spots united, forming an irregular patch). An extreme development of the last-mentioned form has been named ab. extrema, Tutt (see Entom. xxix., p. 341, Fig. 2). Specimens with a sixth spot as in Z. filipendulæ have been occasionally recorded, and an example with the lower spot of the central pair absent has been taken in West Sussex by Mr. W. M. Christy, who has also obtained a number of specimens of a yellow form (ab. lutescens, Cockerell) in the same locality. The yellow form is shown on Plate [148], Fig. 5. Some of the yellow aberrations also exhibit variation in the spots pretty much as in the ordinary form. In some localities, especially marshy ones, the spots on
the fore wings and the hind wings are occasionally dull orange; and I have noted specimens in the Weybridge district, Surrey, with the spots on the fore wings of a pinky ochreous colour, whilst the hind wings were of the usual crimson. Such "aberrations" as those last mentioned probably result from weather exposure. In 1899, Mr. G. B. Corbin recorded the capture, near Ringwood, Hants, of a specimen which had the spots on the fore wings and the red of the hind wings darkened over with dull smoky black, so that the insect when seen at a distance seemed to be wholly black. Dr. Hodgson has recently obtained several of these melanic specimens in Sussex. A form with the spots and hind wings suffused with brownish has been named ab. obscura, Oberthür.
With regard to six-spot examples referred to this species, I am inclined to suppose that they may be the offspring of a chance pairing of trifolii and filipendulæ. That such crossing does occur in nature I have evidence, as on one occasion I found four mixed pairs, the male being trifolii in each case, and the female typical filipendulæ. This was in the Weybridge district, where I had come across a colony of the latter species and was closely examining the specimens for aberrations.
The caterpillar (Plate [145], Fig. 3) is green inclining to yellowish and to bluish, with black marks on the back; a series of black streaks low down along the sides. It feeds on Lotus corniculatus, and on other trefoils and clover: July to May. Sometimes taking two years to complete its changes.