Ian R. Mackay.
A New species of Widow Spider (Genus Latrodectus) from Southern Africa (Araneae: Theridiidae).
Psyche 79(3):236-242, 1972.

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A NEW SPECIES OF WIDOW SPIDER
(GENUS LATRODECTUS)
FROM SOUTHERN AFRICA
(ARANEAE : THERIDIIDAE) .
BY IAN R. MACKAY
Harvard College, 'Cambridge, Mass.*
INTRODUCTION.
Despite numerous names there are apparently only a few species of widow spiders (Levi 1959). The members of the genus Latrodectus are of considerable interest since their venom has a fraction specific to vertebrates, as well as a group of proteins specific to insects, their normal prey. Several new species have re- cently been discerned as a result of studying the habits of sympatric black widows (Levi 1966, McCrone & Levi 1964). Minor but con- sistent differences in the genitalia were found later. Also, Abalos 1962,) found four sympatric species of black widows in Argentina, with different habits and egg-sacs.
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In this paper a new species is described from Rhodesia; the first sibling species of the cosmopolitan Brown widow (L. geometricus). This new species was first separated by the distinctive, smooth egg- sacs (Fig. 9).
The two species seem to occur together. The geni- talia are distinct, in contrast to the sympatric L. revivensis, L. pal& dus and L. mactans tredeckguttatus in Israel (Levi 1966). I have not been able to match this new species to any of the pre- vious descriptions from Africa, most of which are based on color variations of L. geometricus.
EGG-SACS The different egg-sacs (Fig. 9) first made me aware of the possibility of another species confused with L. geometricus. The egg-sacs of L. rhodesiensis are smooth, spherical and dirty white in color (pure white when first constructed). They are larger than the yellow, tufted cocoons of geometricus, with an external diameter of 10-18 mm (5-9 mm in egg-sacs of geometricus from Rhodesia). These smooth cocoons consist of an inner, pear-shaned, thin-walled , - - .
sac - approximately half the diameter of the complete structure - surrounded by a layer of fluffy threads. HEMOLYMPH
In a search for other distinguishing characters I examined the henlolymph of the two species using electrophoresis, since McCrone ( 1967) separated sibling species of L. mactans by this *Mail address: Museum of Comparative Zoology, Harvard College, Cambridge, Mass. 02138.




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19721 Mackay - Widww Spider 23 7
Figures 1-8. Latrodtctus rhodestemis, n.sp. Figs. 1-3, left male pal pus.
1. mesa1 view; 2. ventral view; 3. lateral view. Figs. 415, epigynum. 4. dorsal view, cleared; 5. ventral view. Figs. 64, female abdomen. 6. lat- eral view; 7. dorsal view; 8. posterior view. Scales: Figs. 1-5, 0.1 mm; Figs. 7-9, 1 mm.



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238 Psyche
[September
Figure 9. Egg-sacs of L. r/iodcsiensis (smooth) and L. gfomeiricw (spiked). Lower scale in centimeters.




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19721 Mackay - Widow Spider 239
method. The runs were made on Schleicher cellulose acetate strips in a Shandon Electric cell, with a Vokam SAE 2761 power pack. ,
Borate buffer (pH 8.48) was used and 150 V constant voltage at 3 ma applied for several hours. The results to date indicate that there are differences, for example in the lowered mobility of the last band in geometricus (Fig. IO), but the method is too crude to permit accurate separation.
A difference in the color of the extra,cted hemolyrnph was also noted: that from geometricus was pale pink and from rhodesiensis the hemolymph was colorless.
NATURAL HISTORY The two species are found in the same habi- tat, often living within a meter of each other. No consistent differ- ences have been noticed in the position of the retreat or in the web structure. A qualitative examination of the prey remains of both species has failed to show food preferences. Differences have been seen in the breeding biology. The mean number of eggs per cocoon (in captivity) is different: 133.59 k 39.78
(29 cocoons) for geometricus; and 166.38 å 70.31 (86 co- coons) for rhodesiensis. The diameter of the eggs is 0.91-0.92 mm in geometricus and 0.92-0.96 mm in rh~odesiensis. The color of the egg is different:
those of rhodesiensis are pale yellowish flesh; while eggs of geometricus are dark pink. Kaston ( I 970)) however, has noted eggs of different colo'rs in the same cocoons of black widows. The cocoons of both species are parasitized by the larvae of Mantispa tenella ( Neuroptera: Mantispidae) . No consistent differences were discerned in preliminary observations of the postembryological de- velopment.
Two series of young of each species were reared to the sixth instar (adult males and immature females) and showed no differences in pattern.
Latrodectus rhodesiensis sp.n.
Figures 1-9
TYPES Male holotype, female paratype from Salisbury (Rho- desia), deposited in the Natal Museum, Pietermaritzburg (South Africa). Paratypes deposited in the British Museum (Natural His- tory) and the Museum of Comparative Zoology. DESCRIPTION. Similar in appearance to L. geometricus. Females apparently have similar measurements. The male measures : 2.5 mm total length. Carapace I .2 mm long and I .O mm wide. First femur, 2.3 mm; patella and tibia, 2.6 mm; metatarsus, 2.6 mm; tarsus 1.0 mm. Second patella and tibia, 1.4 mm ; third, 0.9 mm ; fourth, 1.7 mm.




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Psyche [September
Figure 10.
Electrophoresis plates of L. geometricus (1st and 3rd plates from left) and L. rhodesinsix (2nd and 4th plates). 1st and 2nd; 3rd and 4th plates run together. Differences noted by arrows. DIAGNOSIS The males are distinguished from L. geometricu,r by the additional coil of the embolus and by the lack of a spur on the conductor (Figs. 1-31. The epigynum is much like that of geometri- cus. The spermatheme are more heavily sclerotised than in geometri- cus and the coils of the ducts extend antero-laterally beyond the spennathecae (Fig. 4). The inner line of the pattern of the female abdomen seems more distinct (Figs. 7, 8). RECORDS
Rhodesia: I have collected specimens of L. rhodeslemts in Salisbury. Smooth cocoons have been found in Kariba (G. Begg), Darwendale (IRM) and Bulawayo (IRM). I have collected L. geometricus in Salisbury and Urntali.
South Africa: J. Ledger (pers. comm,) collected a single female L. rhodesiensis in WalkervilIe (30 Km south of Johannesburg). G. Newlands has sent me specimens of L. gmetricus from Pretoria (Transvaal) , and Kroonstad and Boshof (Orange Free State). Mozambique: D. Broadley collected a single female L. geomtri- cus with egg-sacs 35 Km south of Inchobe, on the new road to NE Mozambique.
Botswana: There is a single female L. geometricus in the MCZ collection from Tonota (D. Carmichael) . ACKNOWLEDGMENTS I wish to thank my parents, Dr. R. PheIps, Mr. K, Coat-PaIgrave and Mr. B. Lamoral for their help, Mr.



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19721 Mackay - Widow Spider
Map 1. Southern African records of L. rhodesiensis and L. geometricus.



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242 Psyche [September
&I. Oliver made available electrophoresis equipment and I am grate- ful for the photographic assistance of Messrs. P. Holland and K. Korhs.
Dr. A. Hesse kindly identified the coco,on parasites. 1 also wish to thank Mr. and Mrs. J. Coates-Palgrave for their hospitality and all persons who sent me specimens: Mr. G. Begg; Dr. D. Broadley; Messrs. B. Lamoral, J. Ledger and G. Newlands; and Dr. R. Smithers. I also wish to thank Professor H. W. Levi for his help and encouragement with all aspects of this work. The prep- aration of the manuscript and publication expenses were paid in part from National Institutes of Health Grant A1 - 1944 and NSF grant GB - 36161 to H. W. Levi.
REFERENCES
ABALOS, J. W.
1962. The egg-sac in the identification of species of Latrodectus (Black widow spiders). Psyche 69 268-270.
KASTON, B. J.
1970. Comparative biology of American black widow spiders. Trans. San Diego SOC. Nat. Hist. 16(3) 33-82.
LEVI, H. W.
1959. The spider ,genus Latrodectus. Trans. Amer. Microsc. Soc. 128(1) 7-43.
1966. The three species of Latrodectus found in Israel. J. 2001. Lon- don 150 (4) 427-432.
MCCRONE, J. D.
1967. Biochemical differentiation of the sibling black widow spiders, Latrodectus macfans and L. variolus. Psyche 74 (3) 212-217. MCCRONE, J. D. AND LEVI, H. W.
1964. North American widow spiders of the Latrodectus curacavien- sis group (Araneae: Theridiidae). Psyche 71 (1) 12-27.



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