Millipede Hording 



A Curious Phenomenon of Nature 



fry Joseph Hannibal and Cassandra Talerico 



"I Recall Very Clearly the afternoon when our small 

 field party chanced upon this striking mass of mil- 

 lipeds,*" wrote Rainer Zangerl, curator emeritus of fossil 

 fishes at Field Museum and former chairman of the 

 Department of Geology. "We approached a small valley 

 in the eastern bluffs of Indiana's Pleistocene Wabash 

 Valley northeast of Montezuma. An old, rotten barn 

 stood at the mouth of this valley in a pasture. When we 

 got close to the barn we noticed a large number of mil- 

 lipeds in the grass; as we entered the valley, which is 

 wooded with the typical forest of this area, the millipeds 

 markedly increased in number. 



"They were all over the floor of the valley, in many 

 places so thick that one had to look for vacant places to 

 step. The milliped density decreased up the slopes 

 (where it was distinctly drier than on the valley floor). 

 The smell of hydrogen cyanide [exuded by some mil- 

 lipedes as a defense mechanism] in the bottom of the 

 valley was so potent that we did not linger there very 

 long. All millipeds seemed to be adult and of uniform 

 size. There was no way we could have estimated their 

 numbers since many were probably beneath leaf litter 

 and many of those visible were in clumps." 



Zangerl's curious observation, made while leading 

 a paleontological field trip in June, 1959, though 

 not unique, was highly unusual. Similar instances of 

 millipedes gathering in enormous hordes have been 

 recorded in other parts of the world, but no fully satisfac- 

 tory explanation of this truly awesome — even intimida- 

 ting — sight has been put forth. 



Millipedes are multi-segmented arthropods com- 

 prising the class Diplopoda. Worldwide in distribution, 

 they include some 10,000 species and range in size from 

 less than 4mm (about 1/6") long to about 28cm (7"). 

 They differ from their close relatives the centipedes in 

 having two pairs of legs on most body segments; cen- 

 tipedes have one pair per segment. Millipedes (unlike 



Joseph Hannibal is associate curator of invertebrate paleontology at 

 the Cleveland Museum of Natural History. Cassandra Talerico, at | 

 the time this article was prepared, was an assistant in invertebrate , 

 24 paleontology at the Cleveland Museum of Natural History. 



S 



some centipedes) are also quite harmless and they spend 

 most of their time out of sight in dark, damp habitats, 

 such as leaf litter and garden compost piles. Millipede 

 hordes — sometimes called "migrating armies" — have 

 been reported in all the continents except Antarctica. 

 In North America they have been seen in a number of 

 areas, including Illinois and nearby states. 



Hording by the same species seen by Zangerl 

 (Pleuroloma flavipes ' ' ) has been documented a number 

 of times. Frank Young, of Indiana University, reported a 

 June 1957 sighting in the Proceedings of the Indiana Aca- 

 demy of Sciences. His observations were similar to 

 Zangerl's: "When the dead leaves on the forest floor were 

 lifted, hundreds [of millipedes] were uncovered feeding 

 and moving about at every point examined over an area 

 about 30 feet long by 20 feet wide. In places in which the 

 leaf mat was intact one could hear the millipedes feeding 

 below, and the whole area had a distinct odor of crushed 

 cherry leaves due to the HCN gas released from the re- 

 pugnatorial glands of the millipeds." 



Millipede hordes encountered in woodlands create 

 no problem other than possible revulsion or fear — which 

 is not warranted since the creatures are completely 

 harmless, but in areas of human traffic they have some- 

 times been disruptive. Large aggregations on railroads 

 halted trains in Hungary in 1878, in France in 1900, and 

 in Germany in 1906 and 1938. 



Millipede swarms overran residential areas north of 

 Dayton, Ohio, in 1963 and 1964 — events documented 

 byj. M.Ramsey ofthe University of Day ton intheO/u'o 

 journal of Science. He identified the millipedes as Pseudo- 

 polydesmus serratus (like Pleuroloma flavipes, a "flat- 

 backed" species). The millipedes traveled at night and 

 sought cover during the day, Ramsey reported, and their 

 swarms were "a source of aggravation and alarm to a 

 number of property owners." 



In August and September of 1902 an invasion ofthe 

 Ohio State University area, in Columbus, was reported 



" "MiUiped" is an alternate spelling of "millipede." 

 'formerly named Zinaria butleri and Fontaria virginiensis. 



