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       There are many records dating back to the 1800's of arthropods injuring and/or inflicting poisons when in contact with humans and other animals.  Their mere presence may cause irritations and allergic responses.  Matheson (1950) is one of the few medical entomology authors who has presented detailed information on this subject.  He noted that secretions of the salivary glands of arthropods when entered into body wounds can prevent blood coagulation that can cause hemolysis, produce paralysis or act as irritants.  Also, when insects draw blood there is always the possibility that the proboscis may contain pathogens, which if entering the blood stream serious health problems can result.  Disinfections of such wounds is highly recommended.




       Order:  Scorpiones (Scorpionida) -- scorpions:  These animals have a well marked cephalothorax and segmented abdomen that is equipped with a sting and poison gland at the posterior end.  They can be dangerous in warmer regions.  Chelicerae and pedipalps are both chelate.  They have book lungs.  They feed on other arthropods.  They are also viviparous as they bear living young. See Inv150 & Inv151 for examples:



       Some arthropods use venom as a weapon to kill or paralyze when they are threatened.  Humans frequently encounter wasps, bees, ants, arachnids, millipedes or centipedes, etc. that may attack especially if nesting sites are threatened.  Their trailing abdomen that is equipped with a sting easily identifies large arthropods such as scorpions (See:  Scorpion).  Scorpions are especially common in tropical and subtropical areas where some species can attain almost a food in length.  The sting can be very painful but rarely is it fatal.  However, one species in Mexico, Centruroides suffusus Pocock, has been a threat especially to young children, with death ensuing rapidly after a sting.  The stings of yellow jacket wasps and Africanized bees defending their nests not infrequently kill full-grown humans.




       Class:  Arachnida: Order Araneae includes the true spiders.  Segmentation is obscure in the abdomen and there are no obvious appendages except 3-4 pairs of spinnerets at the posterior end of the abdomen that are modified abdominal appendages.  Several examples of spiders may be seen in the following diagrams Inv143 - Inv147:



       Although spiders are generally feared they do not bite readily, but they all possess poison glands and the bites of some species can cause severe irritation and even tissue destruction. 


       The Black Widow spider, Latrodectus mactans Fab. is common in warmer parts of the temperate zone where fatalities sometimes result from its bite.  It is easy to recognize by a jet-black color, a hourglass pattern on the underside of its abdomen and a web that is irregular and without pattern.  Matheson (1950) described the symptoms from the bite as "acute pain, localized and general, profuse perspiration, restlessness, nausea, vomiting, labored breathing and constipation.:"  In tropical areas other species of Latrodectus are considered very dangerous.


       The Brown Recluse or "Violin" spider, Loxosceles reclusa, like the black widow, has venom that causes necrosis of body tissues, which may require drastic surgical removal of the area around the bite.  The common name, "violin spider" refers to a marking on the top of the cephalothorax that resembles a violin.


       Another species that has spread to other parts of the world is the Mediterranean Recluse spider, Loxosceles rufescens (Dufour).  Also, the Desert Recluse spider, Loxosceles deserta Gertsch occurs in the southwestern United States, where its preference for wild habitats generally keeps it away from human habitation.


       Another group of spiders, the Tarantulas (Avicularia spp.), have large species with a hairy appearance that tends to frighten people and animals (See: Avicularia sp.).  Myths about their ferociousness were rampant during the Middle Ages.  However, they are quite tame if not provoked (Baerg 1923) and can even be trained as pets.  Tarantulas are abundant in tropical areas, but they extend well into the Temperate Zone. They are especially active at night as in the Ozark Region of Arkansas, United States where large numbers can crawl all over sleeping campers, but without inflicting bites.




       Subphylum: Myriapoda, Class: Chilopoda includes the centipedes.  They are dorso-ventrally flattened.  Their body consists of a head and trunk but there is no thorax nor abdomen.  The head bears one pair of antennae, one pair of mandibles, one pair of maxillipedes with poison glands at the bases and ducts leading to pointed tips (Note:  these are absent in the Diplopoda).  There are two pairs of simple eyes called pseudocompound eyes.  They have maxillae on the 1st and 2nd segments.  The trunk bears uniramous appendages and there are 15 to 175 segments.  See examples at Inv141.



       Centipedes are also frightening to behold and have caused undue alarm, They possess poison glands although they rarely bite and if so the venom is not very toxic, serving primarily for food digestion.  They are recognized by their many legs on a long body with a distinct head and a pair of many jointed antennae (See: Scolopendra obscura).  Most species are terrestrial, preying on small animals in dark places under logs, leaves and stones (Matheson 1950). 




       Subphylum: Myriopoda, Class: Diplopoda includes the millipedes.  These are cylindrical animals with a head and trunk that is the same as in the Chilopoda.   The head appendages include antennae, mandibles, one pair of maxillae (instead of 2 pair as in the Chilopoda) and pseudocompound eyes on the head.  The trunk has 25-100 or more segments with each segment bearing two pair of appendages.  A fusion occurs between two segments all along the body except on the first trunk segment.  See example at Inv142.



       Millipedes are terrestrial arthropods with a wormlike appearance and many small legs (See:  Millipede).  They have a distinct head with the next four segments being their thorax.  The remaining segments each bear two pairs of legs.  There are no poison glands on their mouthparts, but many species have glands on some segments that produce an irritating liquid, which they can eject for some distance.  This liquid is an irritant that can cause blindness if reaching the eyes (Burtt 1947).


Irritating Moths


       There are also insects that have special hairs, which can cause irritation or allergic reactions (See:  Io Moth &  Browntail Moth).  Some caterpillars of moths and beetles have structures that cause considerable irritation.  Matheson (1950) lists the following Lepidoptera families that belong to this group:  Eucleidae, Megalopygidae, Saturniidae,  Thaumetopoeidae, Arctiidae, Noctuidae and Nymphalidae.  The irritation comes from special spines or barbed hairs that have poison glands.  The barbs can penetrate skin and the poison will spread to produce a rash.  Gilmer (1925) distinguishes two types of poison gland hairs or setae as primitive and modified.  The primitive type has a single seta with a gland cell that opens directly through a pore canal into the hollow of the seta.  The seta contains the poisonous secretion of the gland cell.  These setae retain their urticating properties long after the caterpillar sheds them and their efficacy is not affected by drying.  The modified hair type is found among caterpillars of the Lymantriidae and some Thaumetopoeidae (e.g, brown-tail moth Euproctis phacorrhoea).  Other minute structures occur on caterpillars that can produce rashes.  Matheson (1950) listed a some of the more important   caterpillars that possess urticating structures:




(List derived from Matheson 1950)



Megalopyge crispata -- Flannel moths (North USA)

Megalopyge opercularis -- Puss caterpillars (South USA)

Megalopyge pyxidifera -- Flannel moth (South USA)

Norape ovina --  (USA)

Parasa chloris -- (USA)

Parasi hilarta   -- (Sino-Japan)

Parasa indetermina -- (USA)

Parasa latistriga -- (South Africa)

Phobetron pithicum -- (USA)

Sibine stimulea -- Saddleback caterpillar (USA)



Adoneta spinuloides -- (USA)



Thaumetopoea processionea -- Processionary caterpillar (Europe)


Lymantriidae (Liparidae)

Euproctis chrysorrhoea -- Gold-tail moth (Europe)

Euproctis flava -- (China)

Euproctis phaeorrhoea -- Browntail moth (Europe & USA)

Hemerocampa leucostigma -- White-mark tussock moth (N-Am)

Stilpnotia salicis -- Satin moth (Europe & North America)



Euchaetias egle -- (USA)

Halysidota caryae -- Hickory tiger moth (North America)


Apatela populi -- (USA)

Apatela oblinita -- (USA)

Catocala sp. -- (USA)



Automeris io -- Io moth (USA)

Automeris spp. -- (USA)

Coloradia spp. -- (USA)

Hemileuca lucina -- (USA)

Hemileuca maia -- Buck moth (USA)

Hemileuca oliviae -- (West USA)

Haemileuca nevadensis -- (West USA)

Hemileuca spp. -- (USA)

Pseudohazis eglanterina -- (West USA)

Pseudohazis hera -- (West United States)



Euvanessa atiopa -- Mourning cloak (N. Amer. & Europe)

Vanessa io (Europe)





          Coleoptera include the beetles that have biting mouthparts; the fore wings are modified to form firm elytra.  The hind wings are membranous and folded beneath the elytra, and they are usually reduced or absent.  The prothorax is large and the mesothorax is greatly reduced.  They have complete metamorphosis.  The larvae are campodeiform or eruciform or generally apodous.



       Some beetles that belong to the families Meloidae and Staphylinidae can also cause bodily irritation.  The Meloidae, or "Blister beetles" have cantharidin in their body fluids.  The extract has been used in small amounts as a diuretic and a stimulant to the urinary and reproductive organs.  Blister beetles populations can assume large numbers and do considerable damage to plant foliage. The Staphylinidae, or "Rove beetles", have a genus, Paederus in which there are species that cause blisters if crushed on the body.  Problematic species are Paederus fuscipes (Orient), P. sabaeus (South Africa), P. cribripunctatus (East Africa), P. peregrinus (Java), P. amazonicus and P. columbinus (Brazil), and P. irritans (Ecuador) (Matheson 1950).  The resulting blisters are often slow to heal, so it is best to avoid handling both groups if possible.  However, the benefits derived from staphylinids serving as predators of other harmful insects may outweigh their harmful effects (Moore & Legner 1973)


Bees, Wasps & Ants


          The Apocrita of the order Hymenoptera are included here. The second abdominal segment is constricted to form a narrow waist or petiole, the first segment being firmly joined with the thorax.  Larvae are apodous when full-grown.   Ichneumon flies have slender curved antennae, and there is a stigma on the wing. The ovipositor is generally long and projects forward from the tip of the abdomen. The larvae of Lepidoptera and of sawflies are their usual hosts.



       Insects that have an ability to sting their prey and humans, belong primarily in the order Hymenoptera, which includes the bees and wasps.  Families of the order usually involved are  Apidae (including Bombidae), Vespidae, Sphecidae, Mutillidae and Formicidae.  In the honeybee the female workers have a sting with sufficient poison to inflict considerable pain, even though a bee deploying the sting results in its death.  The hybridization of an African with an Italian strain of honeybee has produced a viscious hybrid, resulting in the death of people in the Americas (See:  Africanized bees) The stings of hornets, bumblebees and wasps are equally potent although the insect does not die after an attack, but can continue to sting repeatedly.  There are many deaths annually among humans and animals that can be attributed to stingings from wasps especially.


       The ants exist as many species and they are numerically very abundant.  Polymorphism is pronounced.  The various social orders in the family have developed around a caste system.  This includes a queen, workers, soldiers, etc.  The workers can appear in different shapes and forms as influenced by nutrition and care among individuals of the colony.  All of the workers are wingless. Some ants, such as the fireant, whose stings are very potent, especially if administered by large numbers in an ant colony.  The ponerine ant, Paraponera clavata Fab., of South America will attack if disturbed, inflicting severe stings (Bequaert 1926).


       The abdomen in this group is rather soft and able to take on a great deal of food, which other members of their colony are able to solicit.  They obtain it by stroking the bearer who then regurgitates the food.


       Colony Establishment. -- New males and females in the colony develop wings, after which they swarm and mate.  The females fall to the ground and chew off their wings, while the males dies.  The female then finds a suitable place to construct a cell into which she will lay eggs.  While waiting for the eggs to hatch, the female does not feed.  She derives nourishment by absorbing internal body parts, such as wing muscles, etc.


       Some species such as the driver and army ants are nomadic.  Conspicuous nests in the ground may be 2.7 meters or more below the surface.  Ants also may live in oak acorns, dry stems, etc.  Their food includes seeds, dead insects, aphid honeydew and household foods.  They may even take aphids into their nests for the winter where they are attended.


       Ant control in houses is possible with poison bait traps.  The treatment of concrete foundations with insecticides is a more drastic approach.


Mosquitoes & Silverfish


       Allergies of varied intensity are associated with the encounter of many different kinds of insects.  Prolonged exposure to the allergen, such as in the bite of Aedes aegypti, can result in immunity to its effects (McKinley 1929).  Some people with special skin properties are also little affected by some mosquitoes.  Serious reactions of a prolonged rash can result from exposure to insects that are generally considered harmless, such as occurs with some species in the primitive Thysanura order of bristletails and silverfish (See:  Thysanura)  



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Key References:     <medvet.ref.htm>


Baerg, W. J.  1922.  Regarding the habits of tarantulas and the effects of their poison.  Sci. Mon. 1`4:  482-89.

Baerg, W. J.  1923.  The black widow; its life history and the effects of its poison.  Sci. Mon. 17:  535-47.

Baerg, W. J.  1924.  The effect of the venom of some supposedly poisonous arthropods.  Ann. Ent. Soc. 17:  343-52.

Benson, R. L. & H. Semenov.  1930.  Allergy in relation to bee sting.  J. Allergy 1: 105-16.

Bequaert, J. C.  1926.  Medical report of Rice-Harvard expedition to the Amazon.  Cambridge Univ., Mass.

Beyer, G. F.  1922.  Urticating and poisonous caterpillars.  Quart. Bull. La. St. Bd. Health 13:  161-68.

Burtt, E.  1947.  Exudates from millipedes with particular reference to its injurious effects.  Trop. Dis. Bull 44:  7-12.

Chamberlain, R. V. & W. Ivie.  1935.  The black widow spider (Latrodectus mactans) and its varieties in the United States.  Univ. of Utah Bull. 25.

Comstock, J. H.  1940.  An Introduction to Entomology, 9th Rev. ed.  Comstock Publ. Co., Inc., Ithaca, New York.  1064 p.

Cornwall, J. W.  1916.  Some centipedes and their venom.  Ind. J. Med. Res. 31:  541-57.

De Villiers, P. C.  1987.  Simulium dermatitis in man:  clinical and biological features in South Africa.  So. Afr. Med. J. 71:  523-25.

Ewing, H. E.  1928.  Observations on the habits & injury caused by bites or stings of some common North American arthropods. Amer. J. Trop.

     Med. 8:  39-62.

Gilmer, P. M.  1925.  A comparative study of the poison apparatus of certain lepidopterous larvae.  Ann. Ent. Soc. Amer. 18:  203-39.

Hoffman, C. C. & L. Vargas.  1935.  Contribuciones y conocimiento de los venenos de los alacranes mexicanos.  Bol. Inst. Hig. Mex. 2(4):  182-93.

Legner, E. F.  1995.  Biological control of Diptera of medical and veterinary importance.  J. Vector Ecology 20(1): 59-120.

Legner, E. F.  2000.  Biological control of aquatic Diptera.  p. 847-870.  Contributions to a Manual of Palaearctic Diptera, Vol. 1, Sci. 

     Herald, Budapest. 978 p.

Matheson, R. 1950.  Medical Entomology.  Comstock Publ. Co, Inc.  610 p.

McKinley, E. B.  1929.  The salivary gland poison of the Aedes aegypti.  Proc. Soc. Exp. Biol. Med. 26:  806-809.

Mills, R. G.  1923.  Observations on a series of cases of dermatitis caused by a liparid moth, Euproctis flava Bremer.  China Med. J. 351-71.

106.   Moore, I. & E. F. Legner.  1973.  Beneficial insects:  neglected "good guys."  Environment Southwest 454:  5-7.

Norman, W. W.  1896.  The poison of centipedes, Scolopendra morsitans.  Proc. Texas Acad. Sci. pp. 118-19.

Parlato, S. J.  1929.  A case of coryza and asthma due to sand flies (caddis flies).  J. Allergy 1:  35-42.

Pavlovsky, E. N.  1927.  The cutaneous poison of the beetle, Paederus fuscipes.  trans. Roy. Soc. Trop. Med. Hyg. 20:  450-51.

Roche, A.J., N.A. Cox, L.J. Richardson, R.J. Buhr, J.A. Cason, B.D. Fairchild, and N.C. Hinkle.  2009.  Transmission of Salmonella to Broilers by Contaminated Larval and Adult Lesser Mealworms, Alphitobius diaperinus (Coleoptera: Tenebrionidae).  Poultry Science 88: 44-48.

Service, M.  2008.  Medical Entomology For Students.  Cambridge Univ. Press.  289 p

Smithers, R. H. N.  1944.  Contributions to our knowledge of the genus Latrodectus in South Africa.  Ann. So. Afr. Mus. 36:  263-313.

Tyzzer, E. E.  1907.  The pathology of the brown-tail dermatitis.  J. Med. Res. 16: 43-64.

Verbeek, F. A. T. H.  1930.  De Canthariden op Java.  Tectona 23:  304-08.

Verbeek, F. A. T. H.  1932.  De ontwikkelings-stadia Van Mylabris en epicauta in de tropen.  Tijdschr. v. Ent. 75 (Sup.):  163-69.

Vetter, R.S., N.C. Hinkle, and L.M. Ames.  2009.  Distribution of the Brown Recluse Spider (Araneae: Sicariidae) in Georgia with Comparison

     to Poison Center Reports of Envenomations.  J. Med. Entomol. 46(1): 15-20.

Walsh, D.  1924.  Insect bites and stings.  J. Trop. Med. & Hyg. 27:  25-26.

Wilson, W. H.  1904.  On the venom of scorpions.  Records of the Egyptian Government School of Medicine, Cairo 2:  7-44.