CHAPTER 4. MARSH FAUNAS 



4.1 ORGANISMS OF TERRESTRIAL ORIGIN 



4.1.1. Insects and Spiders 



Although there are many kinds of 

 insects on salt marshes, they are mostly 

 confined to the higher elevations. Those 

 significant to the ecology of the 

 regularly flooded portions include those 

 that feed on Spartina al ternif lora , some 

 that are associated with detritus, and 

 some that are predators. No group is 

 represented by a large number of species. 



Vince (1979) divided the insect 

 herbivores in Great Sippewissett Salt 

 Marsh into chewers and sap-suckers. The 

 dominant chewer is the long-horned 

 grasshopper, Conocephalus spartinae , but 

 thrips ( Anaphothrips sp.) and crickets are 

 also present. Sucking insects are much 

 more abundant and include plant bugs 

 (Miridae, Trigonotylus sp.), plant hoppers 

 (Delphacidae, Prokel isia marginata , and 

 Cicadel 1 idae, Graminella nigrifrons ), 

 aphids, and scale insects. The latter two 

 types of insects are patchily distributed: 

 rare on another leaf of the same plant and 

 absent a few meters away. They may be 

 locally abundant enough to kill blades of 

 grass. Patches of scale insects may occur 

 30 cm below the level of barnacles growing 

 on Spartina , which indicates they are well 

 adapted to immersion in saltwater (Tippins 

 and Beshear 1971). Prokel isia marginata 

 is the numerically dominant herbivorous 

 insect (by orders of magnitude). It also 

 has 10 times more biomass/m 2 than any 

 other species. 



In fertilized experimental plots in 

 the Cape Cod marshes, the herbivorous 

 insects have become more equitably 

 distributed (smaller differences in 

 numbers of individuals between the 

 different species) than prior to 

 fertilization. There were relatively 



greater increases in the initially less 

 abundant species, i.e., minds, 

 cicadel lids, and grasshoppers. The 

 fertilization increased the nitrogen in 

 the grass, making it a more suitable 

 substrate. This, in turn, led to 

 increased fecundity and survival in the 

 insects. Migration into the experimental 

 area was of secondary importance (Vince 

 1979). Presumably, this equal abundance 

 and distribution occur naturally in 

 productive creekbank stands of S. 

 alterniflora . Vince (1979) believes 

 that the non-creekbank marsh is barely 

 adequate for the maintenance of some 

 of the rarer herbivorous insects. 

 Stiling et al. (1982) have found that 

 leaf-miners in Florida are nitrogen- 

 limited as are the herbivorous insects 

 mentioned above. 



Some insects live within, rather than 

 upon, the Spartina stems. These are 

 usually larvae rather than adults. For 

 example, larvae of otitid flies (genus 

 Chaetopsis ) live within Spartina stems 

 where they eat and kill the terminal bud, 

 thereby causing the death of the shoot. 

 The ecology of such insects is poorly 

 known in New England. Studies in Florida 

 indicate that the otitid larvae reduce 

 competition in their limited environment 

 by stabbing and killing other larvae they 

 encounter (Stiling and Strong 1983). 

 Though the dead larva represents a 

 valuable source of protein, the body is 

 not eaten; i.e., they are murderers rather 

 than predators. 



Other insects found in the low marsh 

 include chloropids, dol ichopodids, and 

 ephydrids. These are all flies that feed 

 on a variety of plant secretions, algae, 

 and detritus both as adults and as larvae. 

 Biting midges and horse flies (such as the 

 infamous "green head") live in the mud as 

 larvae; as adults, the females attack 



17 



