By David McCorquodale, Dean of Science and Technology, Cape Breton University
There is a perception that Nova Scotia and Cape Breton (where I live) may be subject to an invasion of cicadas. The perception seems to stem from the mass emergence of cicadas in the northeastern USA this spring and summer. What an opportunity to build suspense and stress! Consider this headline from Design and Trend on 09 May 2013: CICADAPOCALYPSE: Mass Exodus from the Ground. A Google search revealed dozens of similar, but admittedly not as sensationalist, headlines from news outlets in the northeastern US and a few in Canada.
In my 35 years as an entomologist in Canada I have seen, heard and collected many cicadas. The delightful Dog Day Cicada (Tibicen canicularis) sings from the White Birch trees near my house every summer. It is the species I have seen and heard most frequently. Cicadas are big (some more than 30 mm long, all at least 20 mm long), loud (at least to those who have not lost their high end hearing) and widely distributed across southern Canada. Sound production is fascinating. Males have tymbals under their wings. Tymbals have taut membranes across an echo chamber. The membranes vibrate to produce the high pitched, incessant, droning calls on hot summer days.
However I suspect many people have never seen or knowingly heard cicadas. Why? Probably because most of their life is spent as larvae underground sucking liquids out of roots so they can grow, mature and emerge as adults. Males sing from tree tops, mate with females who then lay eggs on twigs, when the eggs hatch the larvae fall to the ground and burrow to feed on roots. The larvae burrow down among the roots, not to be seem until they emerge as adults.
How can we reconcile these disparate pieces of information: i) cicadas are common and widespread where Canadians live, ii) most people have never seen them and iii) WARNING mass invasion of cicadas this summer!
We cannot because there will not be a mass emergence in Nova Scotia or indeed in eastern Canada. There will be about the same number of adult cicadas in eastern Canada as in any other year. No one will be able to detect a difference in the number of cicadas in 2013 compared to previous years. Perhaps there will be more attention on cicadas — that is a good thing.
How can I say this and go against all the headlines? The first step is to consider what species of cicadas occur in eastern Canada and compare that to which species of cicadas have mass emergences. In Nova Scotia there are three species of cicadas. All three are ‘annual’ cicadas. That is adults emerge each year, mate, lay eggs, larvae develop and then the adults emerge the next year. There are not dramatic differences in the number of adults from year to year. Males sing form the treetops every year and most year most people are blissfully ignorant they are there.
However in the eastern USA there are several species of cicadas (Periodical Cicadas, Magicacada spp.) with a different life cycle. These cicadas also have males who sing, females who mate and then lay eggs on twigs and larvae who feed on roots. But the next step is different, they keep feeding and do not emerge as adults for 13 or 17 years. The adults that emerge are ‘teenagers’, not one year olds. Some periodical cicadas emerge every year, but some years, including 2013 in the eastern USA, there are enormous cohorts of adults that emerge. The timing, evolution and distribution of these periodical cicadas are fascinating (see Magicicada Mapping Project Homepage http://www.magicicada.org/map_project/maps.php, A National Geographic Project).
Legitimately, these intriguing insects are attracting lots of attention. Because many people have a fear (unrealistic in my opinion) of such a large insects there has been undue media attention to the mass emergence, the sensationalist headlines and unfounded stress in some people.
In Nova Scotia there are no reasonable ground to be concerned about a mass emergence of cicadas this summer. The three species of cicadas in Nova Scotia all have an annual life cycle. Numbers of adults that emerge each year are similar. We will not be able to see any difference in populations of adults this year compared to other years.
Despite being able to ally the concerns of Nova Scotians, I feel I am missing a spectacular natural phenomenon. Perhaps this is a reason to relocate from my Cape Breton home? A good one, but there are lots of good entomological reasons to stay.
For more information on cicadas, check out www.bugguide.org (search for cicada) and a paper published earlier in 2013: Biogeography of the Cicadas (Hemiptera: Cicadidae) of North America, North of Mexico by Allen F. Sanborn and Polly K. Phillips in Diversity 5: 166-239; doi:10.3390/d5020166.