Summer is Coming

Summer comes to Hillsborough County, bringing with it a host of implications for our gardens and natural areas. Although we astrologically associate the beginning of summer with the summer solstice, which falls on June 20th, the practical succession of seasons varies from year to year. The National Weather Service provides an excellent overview for South Florida.

Drought-tolerant Atlantic St. John's-wort (Hypericum tenuifolium) is blooming in Bell Creek Nature Preserve, despite the dry weather. Photo by James Robe.

For the purposes of this article, the author defines the Florida summer as when daily minimum average temperatures remain in the mid-70s°F, maximum averages in the high 80s°F, and frequent, daily rainfall occurs. Using weather records from Miami International Airport spanning from 1956 to 1997, they demonstrate that the climate we typically associate with summer begins in Miami by May 21st.

Persistent drought conditions can make gardening difficult. Blue Porterweed (Stachytarpheta jamaicensis), a native butterfly host plant, is doing well in the bottom right. Photo by James Robe.

Although I don’t have their exact methodology, I conducted some rough comparative analysis between historical weather data at Miami International Airport and Tampa International Airport. I arrived at an average summer start date of June 10th for Tampa. For residents of Hillsborough County, the temperature we associate with summer is already here. If you are still waiting for the afternoon showers, perhaps this estimate can give you some hope of relief.

This estimate lines up well with National Weather Service data on rainfall in Ruskin, Florida. Image from weather.gov

A peculiarity driven by summer storms across the world, but especially in our conservation lands, is the iconic sound of the cicada. These droning insects are often heard but seldom seen, and they are poorly understood by many. You’ve probably already been hearing the surprisingly loud calls of the Hieroglyphic Cicada (Neocicada hieroglyphica). Known for its distinctive song, which starts with a series of progressively softer whiny bursts and ends with an even whine, this species is partial to oak trees and is usually the first cicada heard in the spring, continuing into late summer.

Cicadetta calliope, a very small Florida native cicada. Photo by Joselee on inaturalist. BY-NC

The first point of confusion with the onset of cicadas is that there are actually many species of varied sizes, calls, and reproductive cycles. The Little Green Cicada (Cicadetta calliope) is less than ¾ of an inch long and has a high-pitched, pulsing sort of call. This is contrasted with our largest eastern species, Dusk-Calling Cicada (Tibicen auletes), at nearly 3 inches, which has a sound like a motorbike revving up followed by a series of increasingly short bursts.

Tibicen auletes. Photo by Jana Miller

All immature cicadas live underground for several years in a “nymph” stage, feeding on xylem sap from roots. When they are ready to emerge, they climb up tree trunks and molt into adults. The adults are strong fliers and live only for a few weeks, during which time they mate and lay eggs. After hatching, the nymphs drop and burrow underground to start the whole cycle over again.

When Cicada's mold into their adult form, they leave behind an iconic empty shed. Photo by Dankeck.

Periodical cicadas (Magicicada spp.) found in other parts of the United States are known to emerge in massive numbers every 13 or 17 years. Nevertheless, to those reading about them in the news, it may seem Magicicada cicadas are emerging nearly every year. This is because those 17-year cicadas have 12 broods (distinct populations); each brood lives in a distinct geographic area, sometimes spanning several states, and the 12 broods emerge in their own time slot within the 17-year window of their cycle. Likewise, the 13-year cicadas have three broods. This means that nearly every year sees at least one brood of Magicicada emergence in their respective area. These Magicicada emergences are so dramatic because the whole population emerges within a few weeks, rather than spread out throughout the summer.

Observations of Davis's Southeastern Dog-day Cicada (Neotibicen davisi) by month in the State of Florida. Data from www.inaturalist.org

Magicicada cicadas are not found in Hillsborough County, however, many of our local species do still need several years to mature underground. Individuals of every species emerge each year, and the period of their nymph stage is also poorly understood. Cicadas are difficult to keep in captivity for study, and the estimated life-cycle period for local species may range from a couple of years to more than a decade in some cases. The Magicicada cicada emergence is closely tied to soil temperature, triggered when the high 60s°F are reached at a depth of approximately eight inches. The onset of summer is the trigger. This is still somewhat the case for our native cicadas; they emerge over a longer window throughout the warm months.

Drought tolerant plants, such as the wiregrass in this meadow at Bell Creek Nature Preserve, help to prevent soil erosion and solarization during periods of extreme heat and drought, protecting the surrounding biodiversity. Photo by James Robe.

Cicadas are an important part of the food chain all across North America, providing an essential food source for birds, mammals, and amphibians. Yet, they face significant threats from habitat destruction, climate change, and pesticide use. As natural areas are cleared for development, the cicadas dormant underground are either killed or find themselves emerging after their long development into an inhospitable environment. Additionally, chemical pesticide use in conventional landscaping can have hugely detrimental effects.

This wild lupine plant and the wildlife it supports wouldn't be possible without the diversity of other native plants in the surrounding area. Photo by James Robe.

You can help protect cicadas and support their populations by incorporating several conservation practices into your landscaping. Include oaks in your landscaping, as these trees are particularly favored by cicadas. Maintain diverse plantings of native shrubs and forbs to help support insects, birds, butterflies, and more! Minimize soil disturbance around the base of trees where cicada nymphs develop, and mulch with organic materials to protect the soil and maintain moisture. Finally, using natural pest control methods, such as introducing beneficial insects like ladybugs or using neem oil, can help manage pests without harming cicadas.

The Hillsborough County Environmental Lands Acquisition and Protection Program (ELAPP) plays a crucial role in conserving natural habitats that support cicadas and other wildlife. By acquiring and protecting large tracts of land, ELAPP ensures that these ecosystems remain as continuous as possible, connecting populations of animals which under pressure from excess development might become isolated and drop below the required population threshold needed to support the expected biodiversity.

A native Paw Paw shrub in Bell Creek Nature Preserve. Paw Paw are essential for the survival of the zebra swallowtail butterfly. Photo by James Robe.

I look forward to featuring more species and the changes they undergo as the seasons change. Planning ahead for the end of this hot weather, this October, the Hillsborough County Department of Conservation and Environmental Lands Management is partnering with the Florida Birding & Nature Festival to offer guided tours showcasing migratory and local birds through Hillsborough County's conservation lands! For more information on the nature preserves and conservation parks featured, check out the Florida Birding & Nature Festival website to register for the CELM field trips, other trips, seminars, and the expo itself! The festival runs from October 17-20, 2024.