Ptyelus grossus is a bug that is commonly and easily recognised by the white foamy substance (‘spittle’) produced by the nymph or the immature stage as they feed (Allen 2017). They are well known for the phenomenon of ‘rain tree’ produced by the constant dripping of processed tree sap through the bodies of clusters of nymphs and adults feeding on the tree (Picker et al. 2002).
Description/how to recognise it.
A rain-tree spittlebug develops from an egg and transforms into a nymph. The nymphs are found in the spittle foam. The rain-tree spittlebug has a fascinating way of creating its bubbly foam. The body plates, or tergites, form along the sides of the abdomen and meet at the bottom to create a cavity. This cavity acts as a chamber where air can be trapped. The air holes open into this chamber, allowing the insect to take in air; by contracting their abdomen in and out, they effectively create a suction effect. When they release this air through the anal secretions, it mixes with the liquid secretions, resulting in the characteristic foam or ‘spittle’ (Craig 2017). This foam serves to protect the nymphs from predators and helps them to retain moisture.
As young nymphs they are identified by their yellow- and greenish colour with black and grey lines/dots. As the nymphs grow bigger, they turn black with fine cream hieroglyphic-like markings with a central orange stripe. As the nymphs moult into adults, they become large (with wingspan of 30–35 mm) with slate grey wings, marked with two large cream and orange spots and smaller cream dots (Picker et al. 2002). They have a cone-shape end of head, with almost round eyes. Rain-tree spittlebugs have strong hind legs.
Pic: Marlies Craig
Getting around
The rain-tree spittlebug have a unique form of locomotion primarily characterised by its jumping ability – they can jump significant distances relative to its body size. They use their powerful hind legs to propel them away from threats (Marlos & Dhir 2023). The rain-tree spittlebug also crawls along the plant’s surface; they have legs that are adapted for gripping and moving through vegetation.
Communicating
The rain-tree spittlebug uses different ways to communicate. They use vibration on plant surfaces as a signal for readiness to mate or mark a territory. Just like other insects they also use chemical cues, i.e., pheromones, to attract mates. They also display behavioural communication such as jumping and posturing when in fear.
Distribution
Rain-tree spittlebugs are widely distributed in South Africa in all provinces. They are absent from the arid mid-southwestern cape. They also occur in bushveld areas right across the southern half of the African continent (Van Rensburg, 2015)
Habit
Rain-tree spittlebugs are found in subtropical bushveld, forests and gardens. They grow and forage in tress. The ‘rain-trees’ Peltophorum africanum and Philenoptera violacea are favoured hosts, but Tipuana, Grevillea, Vachellia, Senegalia, Searsia, Strychnos and even Eucalyptus species are attacked (Picker et al. 2002).
Food
The rain-tree spittlebug feeds on plant sap by using its stylets (sucking mouthparts) to pierce the tree’s bark and rapidly extract the sap. Since the sap is a diluted mixture of sugars and salts, the insect needs to consume a large volume to get enough nutrition (Hyde et al. 2024). They are often found on specific host plants, such as ‘rain-trees’, but can feed on various other plants, depending on availability. Young nymphs tend to stay close to their feeding sites, often protected by their spittle. Adults can actively search for food. They feed in groups. Like all true bugs, they feed using a specialised structure known as a ‘rostrum’ or ‘stylus,’ which resembles a drinking straw, this can be clearly seen between the legs of the adult, which is greenish with a black tip (Craig 2017).
Sex and life cycles
Sex
The life cycle of a rain-tree spittlebug has three stages, the egg stage, nymph stage and adult stage. The female lay eggs in hidden plant crevices. Courtship behaviour has not been reported. Once the eggs hatch the rain-tree spittlebug nymphs are protected by the ‘spittle’ foam and it also help them to retain their moisture. As the nymphs grow through several instars, they moult and become adults (Marlos & Dhir 2023).
Family Life
Rain-tree spittlebugs adults are generally solitary, but during the nymph stage, they aggregate in areas with abundant food sources, leading to localised populations. They are not known for strong territorial behaviour. Adults may occupy overlapping feeding territories, especially in areas with abundant food. Social interactions are minimal beyond mating and reproductive activities.
Pic: Marlies Craig
The Big Picture
Friends and Foes
Rain-tree spittlebugs share habitat with other sap-sucking inserts; they can coexist because they may benefit from similar conditions. They use certain fungi and bacteria to help them break down organic material, which helps with enriching the soil. The rain-tree spittlebug eggs, nymphs and adults are prey to predators, such as lacewings and ladybugs, which feed on them. If they feed excessively on plants, it can weaken the plant, making those plants vulnerable to disease and other pests.
Smart strategies
Rain-tree spittlebugs main characteristic of creating ‘spittle’s foam while feeding on plants assist in protection against predators and from threat of drying out due to arid weather conditions. Their physical abilities also allows for them to thrive in the ecosystem: they have strong hind legs that give them an advantage when escaping predators. They have a specialised mouthpart known as a piercing-sucking mouthpart. This allows them to feed on plant sap by penetrating the plant’s tissue. The mouthparts are adapted to draw out nutrients. This allows them to feed on any plant/tree they come. Rain-tree spittlebug nymphs and adults display different shades of colours ranging from pale yellow and green to grey and tan This colour variation aids in camouflage, allowing them to blend into their environment and hide from predators (Marlos & Dhir 2023).
Poorer world without me
As part of their ecosystem, rain-tree spittlebugs’ presence and abundance can indicate the health of an environment, which makes them useful for ecological monitoring. Rain-tree spittlebugs contribute to the breakdown of organic materials and facilitates nutrient cycling in the ecosystem. They form part the food web as they serve as food to various predators. They are sap-sucking insects, their feeding may stimulate plant growth and health. They can, however, also cause damage to some plants due to high infestation rates, which may help regulate plant populations. In a nutshell, rain-tree spittlebugs’ role is to maintain ecological balance.
Conservation status
Not known/evaluated. Probably Least Concern due their relative omnipresence.
Relatives
Rain-tree spittlebugs (Ptyelus grossus) belong to the family Aphrophoridae, which includes various species of spittlebugs. These insects are known for producing foamy spittle that provides protection for their nymphs.
Official common name: Rain-tree spittlebug
Scientific Name and Classification:
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hemiptera
Family: Aphrophoridae
Genus: Ptyelus
Species: P. grossus (Fabricius, 1781)
Common names: rain-tree spittlebug; tipuana spittlebug (Eng.)
References
- Allen, J. 2017. Spittlebug: a unique little insect. Bug Week. https://bugs.uconn.edu/2017/07/24/spittlebug-a-unique-little-insect/.
- Craig, M.H. 2017. The soggy existence of the rain tree bug. The Leopard’s ECHO: https://le.kloofconservancy.org.za/the-soggy-existence-of-the-rain-tree-bug/.
- Hyde, M.A., Wursten, B.T., Ballings, P. & Coates Palgrave, M. 2024. Flora of Botswana: Note 20: A note on the Rain tree bug: Ptyelus grossus.
- iNaturalist 2024. Common rain-tree spittlebug. https://www.inaturalist.org/taxa/494314-Ptyelus-grossus
- Marlos, D. & Dhir, P. 2023 Spittle bug: All you need to know in a Nutshell. https://www.whatsthatbug.com/spittle-bug-all-you-need-to-know/ Waterbug.com
- Picker, M. & Griffiths, C. 2002. Field Guide to Insects of South Africa, South Africa. Struik Publishers, South Africa.
- Van Rensburg, J. 2015. Creepy crawlies. Special Nature Event Wild Encounters Kapama Private game reserve: Buffalo camp. https://kapama.com/rangerblog/curious-creatures/
Author: Nompendulo Kristal Mkhatshwa