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<p>The animals on the cover of <em>Mastering the Lightning Network</em> are wood ants (<em>Formica rufa</em>). Commonly used to describe a broad group of ants, “wood ants” are those that either construct nests in forested areas or infest wood in a home. However, <em>Formica rufa</em> specifically refers to the mound-building red wood ants that are mainly found across southern Britain, northern-to-middle Europe, the Pyrenees mountain range, and Siberia. Sometimes, they are also found in North America in both coniferous and broad-leaf broken woodlands and parklands.</p>
<p>Also known as the southern wood ant, this subspecies of wood ants are aggressive, active, and large. The wood ant queens are typically 12–15 mm in size and can live up to 15 years. Worker ants, on the other hand, are slightly smaller at 8–10 mm and have a lifespan of anywhere between a few weeks to seven years depending on whether they’re male or female (males die soon after mating).</p>
<p>Capable of producing formic acid in their abdomens, red wood ants can eject it up to a few feet away when threatened by predators. Their nests are usually conspicuous mounds of grass, twigs, or conifer needles, often built against a rotting tree stump in an area that the sunlight can easily reach. Wood ants live in large colonies that may have 100,000 to 400,000 workers and 100 queens. Red wood ants are very territorial, and known to attack and remove other ant species from the area.</p>
<p>Red wood worker ants forage up to 50 meters from their nest to collect a natural resin found dripping from pine trees. In a behavior unique to wood ants, individual ants walk over the resin to disinfect themselves from bacteria and fungi. Additionally, they also eat aphid honeydew, small insects, and arachnids. Red wood ants are commonly used in forestry and often introduced into an area as a form of pest management.</p>
<p>The red wood ants are currently a protected species and are categorized as “near threatened” by the IUCN. Many of the animals on O'Reilly covers are endangered; all of them are important to the world.</p>
<p>The cover illustration is by Karen Montgomery, based on a black-and-white engraving from a loose plate, origin unknown. The cover fonts are Gilroy Semibold and Guardian Sans. The text font is Adobe Minion Pro; the heading font is Adobe Myriad Condensed; and the code font is Dalton Maag's Ubuntu Mono.</p>