Testacella haliotides and other slugs in an Ipswich garden

TESTACELLA

HALIOTIDEA IPSWICH

A N D O T H E R S L U G S IN A N GARDEN

ERIC PARSONS

Slugs of t h e g e n u s Testacella have b e e n rarely f o u n d in Suffolk, indeed the last r e c o r d refers to specimens of T. haliotidea D r a p a r n a u d f r o m W o o l v e r stone P a r k in 1913. D 체 r i n g 1988 a flourishing colony of this species was f o u n d in my Ipswich g a r d e n . This account notes the discovery and o b s e r v a t i o n s of this u n u s u a l and i n f r e q u e n t l y - s t u d i e d animal.

A n o d d , yellow slug was discovered covered with earth in early J u n e , 1988, as an E r i c a c e o u s b e d was demolished and a p o n d excavated in its place. It was f o u n d when s t o n e s w e r e being r e m o v e d prior to lining t h e hole, and s u b s e q u e n t l y identified and r e c o r d e d as Testacella haliotidea D r a p a r n a u d .

Torchlight searches were then m a d e periodically, a f t e r dark during t h e s u m m e r m o n t h s , f o r m o r e evidence of this nocturnal species, b u t n o m o r e w e r e f o u n d . H o w e v e r , a crushed specimen was f o u n d on the g a r d e n path during d a y t i m e in t h e following O c t o b e r . T h e path is used f r e q u e n t l y , even a f t e r d a r k , and s o m e t i m e s snails, slugs or w o r m s are unwittingly t r o d d e n o n .

T h e y a r e soon e a t e n by o t h e r slug species like Milax sowerbyi ( F e r r u s a c ) , [a species t h a t has b e e n described as 'herbivorous'], Deroceras reticulatum (M체ller) and Limax valentianus (Ferussac). T h e w e a t h e r t h a t day was overcast with drizzle and a g r o u n d t e m p e r a t u r e of 14째C when t h e slug was f o u n d . L a t e r that d a y , a f t e r d a r k , a T. haliotidea specimen was f o u n d on the g a r d e n in t h e s a m e general area. In f u r t h e r searches of t h e whole garden [approximately 200 sq. m.] a n o t h e r t h r e e and the r e m a i n s of a s e c o n d , which was being c o n s u m e d by o t h e r slugs, were located. O n s u b s e q u e n t nights the species was f o u n d on t h e surface of the g a r d e n , for a b o u t a f o r t n i g h t , until t h e w e a t h e r b e c a m e colder (5째C). In early March 1989 a half-grown specimen was f o u n d u n d e r a s a n d s t o n e slab b e n e a t h a plum tree and a n o t h e r , u n d e r surface d e b r i s , a m o n t h later, m e a s u r e d only 15mm when e x t e n d e d [another i m m a t u r e s p e c i m e n was f o u n d in a collection of molluscs t a k e n f r o m a g a r d e n in E a s t o n on the 27th of D e c e m b e r , 1988, at dusk. T h e slug was less than 2 0 m m w h e n e x t e n d e d . ] M o s t of those f o u n d in Ipswich were within 5 yds. of t h e first find, close t o t h e concrete p a t h , and in an a r e a that is part r o u g h grass u n d e r t r e e s and p a r t lightly-forked b o r d e r . T h e y w e r e not to be f o u n d in the m o r e d e e p l y cultivated vegetable plot. T h e topsoil of the g a r d e n is f r e e draining a n d sandy with a neutral p H reading. T h e g r e a t e r area of t h e s u b u r b is b o u n d e d by h e a t h l a n d .

T h e slugs a r e a pale yellow and w h e n e x t e n d e d they m a y be passed at a glance f o r e a r t h w o r m s on the surface at night. T h e body of t h e e x t e n d e d animal is t a p e r e d f r o m a slightly bulbous rear which has on it a small, r u d i m e n t a r y shell. T h i s a p p e a r s only as a small, slightly p r o m i n a n t , oval disc which is n o t very o b v i o u s . Closer inspection, h o w e v e r , reveals t h a t the shell has a f o r m like a m i n i a t u r e Slipper L i m p e t : a shell f o u n d on s o m e Suffolk b e a c h e s . A n o t h e r detail sets t h e species apart f r o m o t h e r slugs, t w o grooves which b r a n c h veinlike a l o n g their length and extend f r o m t h e t o p of the shell

Trans. Suffolk

Nat. Soc. 25

TESTACELLA

HALIOTIDES

A N D OTHER SLUGS IN AN IPSWICH G A R D E N

43

forward along the flanks of the body. Barnes and Stokes have recorded that the eggs of T. haliotidea are ellipsoidal, 7 x 4mm in size, with a white calcareous shell which becomes yellow. In captivity they have been laid in groups of 2 - 1 4 , underground in March, 54-95 days after mating. They also found that embryonic development takes five to six months and confirmed the old Statement that the eggs explode when placed on a warm hand.

The original Testacella was not fully grown when it was found, but with expert advice it has been possible to keep it in captivity since. It has now (March 1989) grown to a withdrawn size of approximately 35mm long by 20mm cross-section with an extended length in excess of 60mm. T h e slug has been kept in a 2-litre, sealed, plastic Container, two-thirds filled with earth, that has a small piece of flat concrete on its surface. This species is predatory and has been identified as a possible biological control of other slugs, however, the specimen has been eating small earthworms exclusively, at the rate of about three every fortnight, and not the immature slugs offered to it of the species found in the garden. It is normally found under the concrete fragment, although at times when the soil has become dry it has been found buried in the soil contained within a papery envelope. It is not very slimy.

Amongst the other slug species of the garden, Limax valentianus is another with few Suffolk records. First recognised in Suffolk in 1986 (Killeen, 1987), it is a native of the Iberian peninsula and is usually restricted to glasshouses in this country. However, in this garden it is thriving outside and is probably the most numerous species. It is also to be found in other gardens of the neighbourhood. It shares a similar lifestyle to that of the other dominant species of slug in the garden, sheltering in d a m p places and feeding particularly on rotting vegetable material. However, it is most fond of Carrion and will leave anything in the compost heap for a bacon-rind. The slug is superficially similar in appearance to some of the common D. reticulatum specimens in the garden, being a medium-sized slug of a muddy-pink colour.

Apart from the dark, lyre-shaped markings on its back, its superior speed sets it apart f r o m D. reticulatum. The extent to which this species is flourishing in this garden suggests that it could be becoming common in other places in Suffolk.

I would like to thank Ian Killeen for his guidance in the study of our garden molluscs and his useful comments on this manuscript.

References Kerney, M. P. & C a m e r o n , R. A. D. (1979). A Field Guide to the Land Snails of Britain and North-west Europe. Collins.

Quick, H. E . (1960). Bulletin of the British Museum (Natural History).

British Slugs (Pulmonata: Testacellidae, Arionidae, Limacidae). Zoology series 16, No. 3 March. British Museum (Natural History).

Barnes, J. F. & Stokes, B. M. (1951). Marking and breeding Testacella Slugs. Ann. appl. Biol. 38, 540.

Killeen, I. J. (1987). Limax valentianus Ferussac (Mollusca: Limacidae) New T o Suffolk. Trans. Suffolk Nat. Soc. 23, 26.

Eric Parsons, 41 Dover R d . , Ipswich, IP3 8 J Q

Trans. Suffolk Nat. Soc. 25

Plate 1: Testacella

haliotidea — a scarce, carnivorous slug common in an Ipswich garden (p. 42).

(Photo: Ian J. Killeen)