虫，状似鼠妇。而大者寸余，形扁如鳖，有甲似鳞，横纹八道，露目六足，皆伏于甲
下，少有臭气，似蜚蠊，本邦未产，此物但华舶来一品，余尝多畜，而使用之，屡得其效。
抵当汤证曰∶少腹硬满。又曰∶有久瘀血。又曰∶有瘀血。
上虻虫三十枚。
抵当丸证曰∶少腹满、应小便不利。今反利者，为有血者。
上虻虫二十枚。
据此二方，则虻虫治瘀血明矣。是与水蛭，互相为其用，故二品等分。唯汤方用三十枚，
丸方用念枚。夫汤之证，急也。丸之证，缓也。故分两，亦有多少也耳。
《淮南子》曰∶虻破积血。刘完素曰∶虻食血而治血，因其性而为用也。按用虻虫之方
曰∶破积血、曰下血、曰畜血、曰有久瘀血、曰有瘀血、曰妇人经水不利下曰为有血曰当下
血、曰瘀热在里、曰如狂、曰喜忘，是皆为血证谛也。然不谓一身瘀血也。但少腹有瘀血者，
此物能下之。故少腹硬满，或曰少腹满，不问有瘀血否是所以为其证也。
虻虫，夏月多飞食人及牛马之血。小者如蜜蜂，大者如小蜩，形似蝇，大目露出，腹凹
偏，微黄绿色，或云水蛭所化，间见之山中原野群集。然则大者山蛭所化，而小者水蛭所化
矣，俱用之。段成式曰∶南方溪涧多水蛆，长寸余，色黑，夏末变为虻。 按∶水蛆，盖水
蛭之误，蛆蛭字相似。
虻虫，形状像鼠妇（一种甲壳类动物）。其中较大的有一寸多长，身体扁平像鳖，有像鳞片一样的硬壳，背部有八道横向纹路，眼睛和六条腿都藏在壳下，带有轻微的臭味，类似蟑螂。日本本土不产这种虫子，这是从中国船只运来的一种药材。我曾经大量饲养并加以使用，屡次获得疗效。
主要治疗瘀血阻滞，表现为小腹部坚硬胀满。兼治发狂、瘀热内结、健忘，以及妇女月经不通畅。
《伤寒论》中抵当汤的证候描述说：“小腹部坚硬胀满。”又说：“有久存的瘀血。”还说：“有瘀血。”
方中用虻虫三十枚。
抵当丸的证候描述说：“小腹部胀满，应当小便不利。现在反而小便通利，说明是有瘀血。”
方中用虻虫二十枚。
根据这两个方剂，虻虫治疗瘀血是明确的。它与水蛭互相配合使用，所以这两种药材用量相等。只是汤剂用三十枚，丸剂用二十枚。因为汤剂治疗的病势急迫，丸剂治疗的病势缓和。所以药量的多少，也是由此决定的。
《淮南子》说：虻虫能破除积滞的瘀血。刘完素说：虻虫以血为食，因此用于治疗血证，是利用其本性发挥作用。考察使用虻虫的方剂记载：如“破除积血”、“下血”、“蓄血”、“有久瘀血”、“有瘀血”、“妇女月经不通利”、“是有瘀血”、“当下血”、“瘀热在里”、“如狂”、“喜忘”，这些都是血证的确实证据。然而，并不指全身都有瘀血。只是小腹部有瘀血时，此物能将其攻下。所以，“小腹部坚硬胀满”或说“小腹部胀满”，无论是否有瘀血，都是使用此药的指征。
虻虫在夏季经常飞舞吸食人和牛马的血。小的像蜜蜂，大的像小蝉，外形像苍蝇，大眼睛突出，腹部凹陷偏斜，呈微黄绿色。有人说它是水蛭变来的，偶尔在山中原野成群出现。那么，大的可能是山蛭变的，小的可能是水蛭变的，两者都入药。段成式说：南方溪涧中有很多水蛆，长一寸多，颜色黑，夏末变成虻。按：水蛆，大概是水蛭的误写，因为“蛆”和“蛭”字形相似。
The horsefly (Machong, 虻虫) resembles the woodlouse (Shufu, 鼠妇). The larger specimens are slightly over one cun in length, flat in shape like a turtle, with a hard shell resembling scales, featuring eight transverse stripes on the back. Its eyes and six legs are concealed beneath the shell. It has a slight foul odor, similar to that of a cockroach (Feileng, 蜚蠊). This species is not native to our country; it is an imported medicinal material from China. I have kept large quantities of them and used them clinically, repeatedly achieving effective results.
Its primary indications are blood stasis (Yuxue, 瘀血) presenting as hardness and fullness in the lower abdomen (Shaofu, 少腹). It is also used for mania (Fakuang, 发狂), heat due to blood stasis (Yure, 瘀热), forgetfulness (Xiwang, 喜忘), and irregular menstruation (Jingshui Buli, 经水不利) in women.
In the syndrome description for Didang Tang (Cistanche and Rhubarb Decoction), it states: "Hardness and fullness in the lower abdomen." It further states: "There is long-standing blood stasis." And again: "There is blood stasis."
The formula uses thirty Machong (虻虫).
In the syndrome description for Didang Wan (Cistanche and Rhubarb Pill), it states: "Fullness in the lower abdomen, which should be accompanied by difficulty in urination. Now that urination is normal, this indicates the presence of blood stasis."
The formula uses twenty Machong (虻虫).
Based on these two formulas, it is clear that Machong treats blood stasis. It is used in conjunction with Leech (Shizhi, 水蛭), so they are often prescribed in equal proportions. However, the decoction uses thirty units, while the pill uses twenty units. The condition treated by the decoction is acute, whereas the condition treated by the pill is chronic or mild. Therefore, the dosage differences reflect the urgency of the pathology.
Huainanzi states: "Machong breaks up accumulated blood." Liu Wansu stated: "Machong feeds on blood and thus treats blood disorders, utilizing its natural nature for therapeutic effect." Examining the indications for using Machong in various formulas: "breaking up accumulated blood," "expelling blood," "accumulated blood," "long-standing blood stasis," "presence of blood stasis," "menstrual obstruction in women," "presence of blood," "blood should be purged," "heat due to blood stasis in the interior," "mania-like state," and "forgetfulness"—all of these are definitive signs of blood disorders. However, this does not imply blood stasis throughout the entire body. It specifically targets blood stasis located in the lower abdomen, where this herb can purge it. Thus, "hardness and fullness" or simply "fullness" of the lower abdomen serves as the clinical indication for its use, regardless of whether other signs of stasis are explicitly confirmed.
During summer, Machong frequently flies and bites humans, cattle, and horses to suck their blood. Small ones resemble bees, while large ones resemble small cicadas. They look like flies, with prominent eyes and a concave, oblique abdomen, appearing yellowish-green. Some claim they transform from leeches. They are occasionally seen swarming in mountains and open fields. Thus, the larger ones may transform from mountain leeches, and the smaller ones from water leeches; both are used medicinally. Duan Chengshi stated: "In southern streams and creeks, there are many water maggots, over one cun long, black in color, which transform into horseflies at the end of summer." Note: "Water maggots" is likely a textual error for "water leeches," as the characters for maggot (Qu, 蛆) and leech (Zhi, 蛭) are visually similar.